How old is Yoshi now? Was he hand-raised/hand-fed? I'm just asking to get an idea of his background and temperament...
You need to start letting him out of his cage every single day!!! And for a good long time each day!!!! You got some really bad advice as far as "not letting your new parrot out of their cage at all until they'll step-up for you, and it's really bad advice for 2 different reasons:
#1) First of all, it's very unhealthy for them, both physically and mentally. He's gotten absolutely no exercise for a month, and it also causes severe boredom, depression, and commonly leads to Feather-Destructive Behaviors...They're birds, they normally fly around 8-10 miles each and every day in the wild, so they cannot be just kept inside of a cage for a month at a time. Period. Not your fault, you just got horrible, horrible advice...
#2) You've been working with him/trying to train him to step-up while he's inside of his cage, his "territory", and by constantly putting your hands inside of his cage, or his "territory", and this is no-doubt why you're moving in a backwards-direction in-regards to bonding with him, because in-order to bond with a parrot, any parrot, and also in-order to be able to teach them to simply step-up for you on a regular-basis or on-command (should just step-up for you whenever you put your finger down at his belly right above his feet ultimately), you must first "Earn Their Trust"...And every time you're putting your hands inside of his cage or his "territory" while he's also inside of it, and you're spending time with your hands inside of his cage trying to get him to step-up, meaning you're putting your hands extremely close to him and trying to touch him, you've just been reversing any Trust-Building that you originally did with him (also remember that he literally hasn't been ouside of his cage in a month now, so he's quite familiar and protective of it I'm sure)...
The reason that I asked how old Kermit is was because I wanted to know whether or not he is of an age where sex-hormones are also an issue; for Green Cheek Conures puberty usually starts between the ages of 8 months-old to around 1 year-old, usually it happens right around 1 year-old. However, if they have anything inside of their cages that is a "Trigger" for hormonal-behavior, then they tend to go into puberty much earlier than they normally would (They should not have ANYTHING inside of their cages that creates a small, dark place that they can get inside of or underneath ("Nest-like"), nor anything that could be seen-as or used-as "Nesting-Material", as these are one of the most-common hormonal "Triggers", and unfortunately they are sold by pet shops as being safe and wonderful for pet birds)...So if Kermit has ANYTHING inside of his cage like any type of "Bed" (they sell those "Triangle-Beds" for birds in pet shops), any type of Tent, any of the "Happy" or "Snuggle" Huts (they are actually extremely dangerous and kill thousands of pet birds for other reasons, so they need to be thrown away immediately if he has one), any type of Hammock, any type of "Box", meaning a cardboard-box, a nest-box, etc., then you need to remove them from his cage immediately and not ever put them back inside...And as far as "Nesting-Material", I'm talking about any type of animal-bedding or anything similar that is often put in the bottom of a bird's cage to absorb their droppings, such as rodent bedding, wood-chips, corn-cob bedding (which they stupidly and irresponsibly market as being "for birdcages"), crushed walnut-shell bedding, shredded-paper bedding (such as "Carefresh"), etc. You only want to put either sheets of clean newspaper, sheets of Butcher's Paper, or actual birdcage-liners in the bottom of his cage, and they need to be UNDERNEATH THE GRATE so that he cannot access them and start shredding them into "nesting-materail"...
**Also, try not to ever pet/scratch him anywhere on his body except for his head, face, and the back of his neck (and with some birds under the chin is also okay, some not, it depends on the bird). Touching/petting/scratching your bird on the back, the wings, under the wings, anywhere on his chest/belly, his legs, tail, or anywhere around/near his Vent will also trigger hormonal-behavior...
***So, forgetting the sex-hormones for right now (that was just an FYI kind of thing), what you need to do is first of all, if you haven't done this already, you need to make sure that his main-cage is located in the "Main-Room" of your home, which means the room of your home where you and the others who live with you (Kermit's "Flock") spend most of your time whenever you're at home. This is extremely important with pet parrots when it comes to first Earning Their Trust, Bonding-Closely with them, and also just simply keeping them Psychologically and Physically happy and healthy. Parrots are all "Flock Animals", and as such they need to always be with their Flocks...You and whomever you live with are his "Flock", and even though you might not be paying direct-attention to him or interacting with him all the time when you are home (just like all the birds in a Flock aren't always talking to each other all of the time), he still wants and really does NEED to be around you/near you/with you or whomever else in his Flock is home. So that means that when you and the rest of the people you live with are at home, if the room you all usually hang-out in is the Living-Room, Family-Room, Den, TV Room, etc., then that is exactly where his main-cage needs to be (I say "main cage" because some people also have a much smaller, free-of-toys "sleeping cage" that they usually put in their bedrooms that their birds sleep in beside them, which is totally fine)...So whenever you or any other people who live with you are at home watching TV, on the Computer/Phone/Tablet, are Gaming, are talking with each other, are eating a meal together, having visitors over, etc., then it's extremely important that Kermit is in the same room with you so that he feels like he's a part of the Flock, and also of course because the more he's just around you, sees you, hears your voice, has you and others walking past his cage (his "territory" again), etc., the more comfortable he's going to be with you...And the more likely he'll be to entertain himself inside of his cage with his toys....Some people make the mistake of putting their new bird (the only bird they have) in a spare-bedroom or some other back-room in their home, thinking that it's going to be really nice to make it into the "Bird's Room". Sometimes they go all-out and really set-up a really awesome Bird-Room with perches all over the room, swings, all kinds of toys hanging everywhere, a window perch they can look out of all day long, etc...And then their bird does nothing at all every day, all day long, but sit in one spot and continually cry/scream/yell, because they know/can hear that someone is at home, but they can't see them, and they are feeling left out of the Flock, and they don't want to entertain themselves or look out the window, etc. because they just want to be with their Flock...And the other common result of this is the bird just turns into a silent statue that makes no noise, but also doesn't move, doesn't play with anything, doesn't fly around, etc. They just sit in one spot all day long, every day, and that's their life besides eating and sleeping...
If you've already got Kermit's main-cage in the "main-room" of your home, then the next step is to start letting him out of his cage every single day, for ideally 4-5 hours a day, and for you to start working on Earning His Trust and teaching him to "Step-Up" for you AFTER you Earn His Trust...But you're most-likely not EVER going to accomplish this as long as you keep putting your hands inside of his cage and attempting to train him that way. The first thing that I suggest that you do is to either buy or build him (or re-purpose something you already have) a "Stand/Perch" of some kind that you can put in the main-room of your home next to or near his main-cage, that he can automatically start flying to (or if he's clipped that you can transfer him to) whenever you open-up the door to his cage...Because that's going to be the idea, that every day when you're home you're going to simply open-up the door to his cage and then you're going to wait for him to come-out on his own...And the very first time he does this you need both verbally-praise him a lot, AND give him a "Training-Treat" (whether he comes out and climbs on top of his cage or he comes out and flies onto something else, either way)...
A Training-Treat is his absolute favorite treat (and something that he can eat quickly and that you can keep in yoru pocket or near you at all times so that you can reward him quicklly), and it's something that you only give him as a reward when he does behaviors that you want him to do (Positive-Reinforcement)...Raw, unsalted Sunflower Seed Kernels are good Training-Treats (he shouldn't be eating Sunflower Seeds as a part of his regular diet as they are nothing but fat, but if he does then they cannot be his Training Treat)...