For most wounds I would recommend cleaning it with betadine, and applying plain antibiotic ointment. Vetericyn can also be used instead. Watch for any pecking by other chickens, and separate temporarily if needed.
Thanks. We just cleaned it with warm Dawn water. Pulled off the scab and it's much worse than we thought. It's his whole bottom end. I cut his feathers so they don't get imbedded in the scab again. Put triple antibiotic on it. He's in the house in his own tote with a clean towel. Did I miss anything?