Watch for any redness or swelling that might indicate bacterial infection, feed healthy foods and let the fishes immune system handle the rest. In a healthy environment, that should heal up just fine with no intervention on your part. You might consider doing something to curb your tangs aggression, try moving some decorations around (it doesn't really work all that often, but it does sometimes and is easy), or removing the fish to another aquarium for a week or so, then put it back in.