Hello and welcome!
So sorry you’re having to deal with this. Several of us are loved by pluckers and barber era so you’re definitely in good company.
Can you give us your macaws backstory? Show long has he been with you? How long as he plucked? What is his diet like? Daily routine?
Plucking is a very complex behavior that can have its roots in hundreds of causes. We need information to help guide.
The honest truth is that much of the advise you’ll get will fall into a few key camps: 1) take the bird for a full physics by an avian certified vet to rule out any medical causes, 2) simply providing a loving home, 3) provide daily enrichment/play/foraging opportunities, and 4) improving the diet.
Added bonus recommendation: a soothing spray is occasionally recommended as well. If the skin is highly irritated, a soothing spray like Avicalm can help sooth irritated skin, which may give a fighting chance. However, be wary of anything that claims to fix plucking with a bottle.
However, if he’s been plucking for a long time, you can address the underlying synotoms, but it’s been so long that the plucking will be an ubreakable habit. As my vet says, “so long as you’ve fixed the cause, there’s nothing wrong with a naked, happy bird!” One might argue to never give up hope, and the constant search for a cure will be immensely beneficial to your bird. but there is a reality to bear in mind that it might not be correctable.