I had a chicken with a wound like this a few years ago. Took her to the vet and he recommended that I run warm water over the wound twice a day for 15 minutes each time, then put Silvadene on the wound(I’m sure you could use neosporin as well; Silvadene is used on burns and I had some here). She healed up beautifully. Her wound was big and it got pretty ugly, but she healed. I hope this helps with your rooster.