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You need to rub some coconut oil or vaseline on your birds bare butt. This will help if there is any redness or infection.
For ways to stop this pecking you need to make sure that the birds have lots of room. They should have 8-12 square feet per bird in their run and 3-5 square feet per bird in their coop. Also, boredom busters will help keep the pecking at bay. Hanging treats, greens, roosts, ladders, dirt, leaves and stumps are all great to use.
Pinless peepers can help too.
Best of luck!