Is he biting aggressively, or just using his beak to stabilize while he gets on your finger? I've had friends say that Puck was "biting" when was doing that, even though it didn't hurt. Their beak is like a hand to them.
If your bird isn't comfortable enough to step up, spend time with him, and let him get comfortable with you, without expecting him to step up. Be patient. Birds are smart. They need their boundaries respected as much, if not more than we do.