If you have all hens, just put him in with them and keep an eye on them. If you have another rooster, take the hens out of the run, and put a barrier between them for about a week. You have to move the hens somewhere else, or the roosters will fight over them.
EDIT: I'm not saying put him in quarantine. I'm saying if you have a rooster already, put a barrier in the run and let them see each other before you put them together. Hens present make them more aggressive.