To the OP, this is my advice:
I've never had to retrain a bird that I've owned from a baby out of a biting habit because I have never given them reason to develop one. Babies will nibble on fingers and I correct that, but that's not biting, it's beak exploration, which is completely natural. When they're doing that, you redirect their attention to something appropriate to chew on, or you put them down so they learn that doing it loses your attention, which generally they want (unless they are afraid of you, but if they're afraid of you, you wouldn't be at this stage of having them on your hands anyway if you're handling things correctly).
I've never had to train any out of biting because I never gave them a reason to bite me. I have never caused a fear bite or an aggressive bite if the bird is giving warning because I read their body language, respect it, and don't force myself on them. And because I never cause a bite that way, I never have to train them out of realizing that biting humans causes humans to do fun things, so they bite for the reaction. That's the hardest biting habit to break, and you don't want to get your bird into that habit, so when you do get bit, don't react by yelling or shrieking or jerking your hand away. These are all fun things to the bird.
To give one example, the 13 year old cockatiel I adopted never once bit me. He was described as "mean" and a biter by his former owners. This was because he was biting out of fear and his former keepers did not respect what he was telling them. I simply worked with him slowly, respected his body language, never forced him to do something he didn't want to, and he never bit me. 13 years of being mistreated and biting, and he never bit me, ever, because I respected what he was saying to me. One month of that and he was my best friend, no biting, I was able to switch him onto pellets after a lifetime of a poor diet on seeds which is not an easy thing to do, and he trusted me completely.
This is not to say I've never been bitten, because I have, and they were all from birds who either learned to stop warning a human a bite was coming because their warnings were never heeded in the past so they go straight to biting, or because the bird was over stimulated and I didn't pay attention to the signs. The latter was entirely my fault.
So pay attention to your bird's body language. Find out why it is biting and then from there you can figure out what you need to do to correct it. This advice comes from many years of working with many parrots, some previously abused.