First, as everyone says, patience. But that doesn't just mean patience long term, but in every moment when you want him to do something and he doesn't want to. Pionus can be very shy birds. When people are trying to tame a bird I like to put it in this perspective; how long would it take a grizzly bear to convince you to let it hold you, pet you, feed you, and just in general for you to trust it. A long time, right? Because it is a predator and you know it! So every time your bird doesnt want to do something, just imagine a grizzly bear trying to get you to climb onto it or take food from its claws. This doesn't mean give up, it just means be compassionate and understanding.
Also, any bird who is old enough to perch and is falling off his perches needs to seed the vet RIGHT NOW.
The diet needs to change, and it will help more than you know. Slowly adding fresh food has never worked for me, but I have successfully switched dozens of birds, including the most hard-core of seed junkies, to fresh diets. There are many people with many strategies, but I will share mine with you, as it works for me every time. But first, let me emphasize that DIET MATTERS! Not just because hih want your bird to be healthy, but also because we know even from human studies that a bad diet leads to feeling bad, and a good diet leads to feeling good. A bad diet could be leaving your bird feeling sick all the time, or just in a brain fog, or without energy, and none of these are good for your relationship, or for training. The other thing is that you are very likely feeding him what would be his favorite treat in his dry mix. Would a cupcake motivate you if you are burgers, fries, and cake for every meal? No! Right? But how about if you ate a really good diet of mostly veggies, then a cupcake might seem like an enormous treat! For example, many of my birds with do ANYTHING for a peanut or sunflower seed, but before I switched their diet I could not get them interested in any food treats enough to be useful for taming or training. On that note, cheese is a bad idea. Dairy is only acceptable in the TINIEST amounts, no matter how tiny the pieces, even once a day is too much.
So how do you change the diet of a stubborn bird? The first step is sprouts. There are threads here on how to do it, and videos and manuals all over the Internet so I won't go into it here, but you can sprout the seed your bird is already eating for starters, just be sure to remove any pellets first as they can make the sprouts spoil. Switching from dry seed to sprouted seed is thei easiest, cheapest, and best first step you can take in my experience, and most birds LOVE it right off the bat! If your bird regents it for two days (which i have never seen happen) you may want to take a step back and just start with soaked seeds before moving to actual sprouts.
Once your bird has been eating the sprouts for about a week, you can start adding in veggies. Most effective way I have found to do this is to chop up as many safe veggies as you can, as small as you can. The size of a pea is the biggest you want when you first start out, and smaller is better. Food processors, juicers, and blenders are really helpful here. Focus on dark leafy greens, peppers, carrots, broccoli, dense veggies not watery ones if possible. A favorite of all my Pionus is edemame. Begin mixing the veggies in the sprouts, you can start with about 1/4 of the food being veggies, and work your way up to however much you want. I like to feed about half sprouts and half veggies for most of my birds.
Some people really encourage pellets, and I think it is wise to teach all birds to eat pellets just in case they someday move on to a new home where the owner doesn't take the time to feed them fresh food, or in case you hit a rough spot in your life temporarily, because pellets are better than just dry seeds, but they don't come anywhere near the. Nutritional value of fresh and live food, just as you can never replace veggies in the human diet with "health food bars."
All these things will help with taming. Also, how much does your bird move around the cage, play, and interact with his environment? When I first got my Maxi's they were the ultimate perch potatoes, eating pellets and sitting there doing nothing.switching them to live food and teaching them to forage brought out their personalities and returned their food drive which is excellent for training.
Some more questions, does he bite you when you try to get near him, or does he just move away? If the answer is move away, just continue being near him and talking to him, moving slowly when you are cleaning his cage or things like that, and gradually getting your hand nearer to him to offer treats. I find birds are usually much quicker to take a treat from between cage bars, because it offers them a barrier and a sense of safety, so start there. Don't be surprised if he doesn't take a treat until his diet is switched away from seeds. Once he takes treats from your hand, start target training as has been mentioned. Research how to use your clicker, but don't let him near the sound until he is taking treats from your hand, and you know how to use the clicker properly.
