Get a treat cup. Put the treat cup either at the front of the cage or on the side. Every time you walk by the cup, put Schin's favorite treat inside the cup (after you figure out what that is - sunflower seeds, safflower seeds, millet, or?).
After a few days of this, try giving Schin the treat by hand through the cage bars.
If he readily accepts this, then move on to giving the treat through the cage door. Once he becomes comfortable taking treats from you, you can then ask him to come to the door of the cage to receive his treat.
Once he's comfortable with this step, you can then put your hand at the cage door (or perhaps just resting on/against it, with it open) and offer a treat with your other hand above the one you want him to step on. Allow him to reach over the 'step' hand to receive the treat. If he's fine with this, have him reach further for the treat. Then reach far enough that he has to put one foot on your hand. Then reach further that he has to put both feet on your hand.
If at any point in time he becomes uncomfortable or backs away, go back a step.
I used the hand at door method with an already tame but biting green cheek, although instead of having her taking the treats from my hands, I actually had her take the treats off the back of my hand and I strategically placed the treats further back onto my arm, so if she wanted the next treat, she had come further out of her cage for it. Her owner couldn't get her out of the cage without biting and couldn't handle her without her biting. In one session/day (first time meeting this bird), I was able to get this green cheek out of the cage without biting and even had her up on my shoulder and got her to step down without biting. I worked with her in a manner that she was willing, if hesitant about.