Other than take him to a vet, about all you can do is put him in a warm, protected place by himself (like your bathtub) and hope he will recover in the rest and quiet. These birds will go into a sort of shock when injured, and sometimes they just come out of it and begin moving around again. They may not eat or drink til the shock goes away. On the other hand he could have serious internal injuries and be about to die, regardless of what you do.
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It doesn't need a bandage on his back. If there is a wound or raw skin, just clean it gently with warm soapy waer or saline and put a little Neosporin on it, or whatever you usually do for first aid at your house. Just be sure you don't use any ointment or cleaner that has a "caine" drug in it, like cetacaine, benzocaine, etc.