I have a Hahn's that was a rehome. Same issues as you're describing.
He had a fear of my hands for a long time, and still, can get very aggressive if I move too fast.
I was lucky as he's food motivated, so that really helped. Pretending to eat a favorite treat of his in front of him would "lure" him close to me, then, bit by bit and over time, in order to get the treat he had to step up to a training perch, or my arm. He seems to do a lot better if he steps up to my arm, instead of to a finger/hand. Besides, he can do a lot less damage to my arm than he can to my fingers.
I was also lucky as he loves being out of his cage. I know many may not agree with my tactics, but .. from the beginning, in order to come out he had to step up .. not necessarily to my arm, but at least to a training perch.
Each time he stepped up the the training perch, he got a treat. When he didn't want to step up, and lunged or tried to bite, I quietly walked away. When he did step up to the perch, it was much easier to get him to step up to my arm/hand from there without fuss.
He loves attention, loves scritches <to a point, gotta watch him cause he'll decided he's over rather quick and give a good nip when he's done with you>.
He's now progressed to flying to me for attention, when he wants it of course. He's been flighted for a long time, but is really a horrible flyer .. although, that's getting better as well.
He's to the point where he will step up to my arm from inside the cage about 99% of the time without pause <usually he's about ready to jump out at me .. lol>. He's about 90% when it comes to stepping up from other places, like his playtop, playstand, back of my chair .. etc. He's bossy . he's a Hahn's .. lol .. and wants to do things on HIS terms.
Usually when he's being a butthead about stepping up, all I have to do is eat an almond in front of him .. that pretty much does the trick <he's an almond junkie>. I don't think he'll ever be 100% comfortable with hands, esp. hands moving too fast, but he's come a very long way from the scared little bird he once was.
Just seeing him have the confidence to fly across to someplace he wants to go is a wonderful thing.
So, I guess I'm recommending treats .. lol .. if your guy is food motivated, starting with a training stick, using your arm more than your hand, and of course lots and lots of time.
Oh .. btw .. I've had him for just over a year now.
JMHO