Why don't you go to
www.behaviorworks.org and read some of the articles there? Biting is not a natural behaviour for a bird, humans teach them to bite. You give your bird choices just like you like to make choices about what you do. The more positive interactions you have with your macaw, the better the relationship. And 4 months is not a lot of time. Took me 3 years to have a wonderful relationship with my rehomed Timneh. I didn't push her, respected the fact that she did not want me to touch her stuff and rewarded her often. I used pine nuts, almonds and for a treat to be really valuable it must only be used as the consequence for a wanted behaviour. Works like this.
Antecedent: Bev asks Gypsy to step up
Behaviour: Gypsy steps up
Consequence: Bev gives Gypsy a pine nut
Possible Future Behaviour: Gypsy will step up more often to get a pine nut.
And Gypsy only gets pine nuts as a reward. They are not in her usual diet.
Always remember. Behaviour has function. When you ask and I do mean ask your bird to do something, ask yourself this "what is my bird getting out of it". If he/she is not getting anything out of your request, why should they do it. Just because we say so? That's how we get bitten, because we push too far. We demand good behaviour when we really need to earn it.
Bev
There is no creature on this planet that will help you find your inner child as quickly as a parrot.