Greetings, I am Dr. Pat. I have worked with birds for many years. I will do my best to help you. I am sorry no other expert has taken your question. We all come online at different times, I have just logged in and saw that you have not been answered. I hope I can still be of assistance.
Firstly I would worry that something is very wrong and he is either irritable or in pain. ANY change in behavior is worth a visit to a vet with geriatric bird experience. He certainly should have a range of diagnostic tests run.
Has there been major change: hosuse renovations, new people, pets, guests, etc? New diet? Any accidents or mishaps? Is therre anything that you do that seems to trigger this behavior? Has your life changed or are you having any problems he may be picking up on?
In Amazons the most likely cause of acute biting is spike in reproductive hormones. If this has not happened in the past, I would really worry that something unusual is causing excessive hormmone production--such as reproductive tumor, nutritional upset, metabolic disease, sleep deprivation or a combination of all the above. And these need to be sorted out by a series of tests.
If this were my patient, and money no object, I would start with complete fecal analysis and direct smear, stained with Sedi-stain and unstained for multiple parasites, fungi, spirals; direct smear stained with Sedi-stain and unstained of the oral cavity; bacterial culture and sensitivity of the feces and choana. Depending on the case I might do a fungal culture. Routine blood work is necessary to rule out other issues. There are MANY DNA/RNA tests for bird diseases. Ultrasound would be my first choice, rather than radiographs, to check for reproductive tumor/abdominal organ health.
To help moderate the aggression, he needs:
1)excellent diet (see below for guidelines)
2) health check
3) 14 hours DARK, QUIET UNINTERRUPTED SLEEP AT NIGHT (no TV, people, lights on, nocturnal disturbance by people, pets, rodents, insects, noises)
4) diversions, toys, excersize, outdoor time
Even if his entire lifestyle changes and there is not any disease, it will take a good month for things to calm down, so number
5) patience abnd understanding.
I know it is expensive, but you may not have many home options, because the first thing you need a vet for is to find out what is going on. Treatment is only as good as the diagnosis. If you call around, you may find a vet to work within your means.
I really must stress that you need a bird-experienced person, and not just a vet who advertises that they care for birds.
You need to take your bird to see an avian-experienced veterinarian ASAP for complete examination, diagnosis and appropriate treatment.
Online you can check to see if this https://companionparrotonline.com/beak_book_detail.html is available; it has some practical solutions to common behavioral problems.
He needs something to do with his mind. You can read children's books to him, point out the pictures, show him garden catalogs, teach him to count, anything to make him educated.
Talk to him like an 8 year old kid. If he doesn't want to step up, explain that he needs to cooperate. NO DRAMA. walk away if he doesn't. Then come back and ask if he wants to step up, again. Use the same command and be consistent, not afraid, gently assertive, and NO DRAMA. Did I mention NO DRAMA?
Here are a few suggestions that I give everyone: important!
The following guidelines help with basic issues such as nutrition, obesity, good immune status. Surprising how the following can make a bird healthy, and how infrequently birds are ill if they are on the following regimen. No amount of medicine is going to work if the birds' basic needs are not met.
Birds should be on a high-quality, preferably prescription, pelleted diet: I prefer High-potency Harrison's
In addition, they should be offered dark leafy greens, cooked sweet potatoes, yams, squash, pumpkin; entire (tops and bottoms) fresh carrots and so forth. No seeds (and that means a mix, or millet, or sprays, etc. etc.) and only healthy, low-fat high fiber people food. A dietary change should be closely monitored and supervised by your avian vet.
Birds should get 12-14 hours dark, quiet, uninterrupted sleep at night. Any less and they can suffer from sleep deprivation and associated illnesses. They should be covered or their cage placed in a dark room that is not used after they go to bed.
The cage material should be cleaned everyday, and twice a day if the bird is really messy. Paper towels, newspaper, bath towels are ok. Never use corn cob, sawdust, wood chips, or walnut shell.
Food and water dishes should be cleaned and changed daily. Keep one set cleaned while the other is in use.
Fresh, perishable food should be placed in separate food bowls. Remove fresh food from the cage after a couple of hours to avoid spoilage.
Change cage papers daily, and clean the grate and tray weekly.
Clean food debris or droppings from toys and perches as needed (which can be as often as once a day).
Grit is not necessary for birds, and will cause digestive problems and death. The best sources of minerals (and vitamins) are leafy greens. Never give grit, gravel sandpaper or cement perches. A bird will eat those to excess when it is not feeling well or if there is a nutritional deficiency. They do not need it at all (an old myth from the poultry days, even poultry do not need it). It can cause an impaction and lead to serious or fatal consequences.