Yes, stick training as Lori said would be the first thing.
Other things to keep in mind: birds don't want to step up to an unstable perch, they aren't dumb, they see our hands and fingers flailing around all day then we ask them to step up onto a finger. Mojo needs to learn to trust you, and trust that your hand/finger is a stable perch.
Auggie was well trained for the step up, then suddenly he quit stepping and would just chomp down as you are describing. There are two things I did to get past that. First, I changed his view of my hand: Instead of offering one outstretched finger I kept all my fingers together (karate chop style) and he seemed much more comfortable. I don't suspect this will be the case for all birds, but do try different things as you never know what will work. Another benefit of changing the view of the hand is if there is a habit established of SEE OUTSTRETCHED FINGER -> BITE FINGER then changing the view of the hand is changing the stimulus and hopefully avoiding the pattern.
Secondly birds do not take well to surprises. If Mojo has had some training in stepping up then give a good clear command "step up" before your hand goes near him. Basically he thinks "step up? WHERE? ... OOOH there." rather than "What the heck is that hand doing? I don't care what you're saying, Im biting."
Lastly be patient and give him time. A change in surroundings is stressful for a bird. Even without much work with stick training or anything else Mojo will likely warm up to the idea after a week or so. Don't force anything at this point. If he doesn't want to come out of his cage yet don't worry. Let him get used to seeing you as the one who brings food and treats every day, cleans the water dish, etc etc. Let him learn his surroundings aren't going to change again and he will warm up to you when he realizes this new place is home.
