Im working with a mini macaw (hahns)?

he i was told was terrorized by little people and isn't real trusting with anybody bites real hard putting it mildly,i also think adults did the same thing with him after he started defending himself he is 4 so i have been told he also wants to be with people but feels he has to draw blood,he isn't responsible for what he does!i have helped biters before but not this bad.im not going to stop trying he is a Diamond in the ruff and needs my help and i need yours please