It’s tough.
You can try teaching him to displace his biting – offer him something that he likes to chew on whenever he seems to be inclined to bite.
You can also use mild negative reinforcement. Yelling or physical retaliation won’t work. What you have to figure out what makes him uncomfortable and use it when he bites. A sharp puff of air in his face (blow on him), a sensation of falling (drop the hand that he’s sitting on a couple of inches) – whatever you do, you have to be consistent.
And, of course, be sure to reward him when he is behaving – treats, affection, whatever works.
Hand raised babies can actually be tougher – they don’t get the social training from their peers that other birds do. As a social animal, the would normally get feedback for inappropriate behavior (i.e., they’d get smacked for biting).