How do you get rid of acne ON scar tissue?

My little brother had an unfortunate accident while biking home from the bar one night and has a good deal of scar tissue on his face. Nose is no longer broken, teeth are fixed, but skin takes a while. What he’s having an issue with now is acne on the scar tissue. Obviously this is delicate new skin and what works to keep him from breaking out elsewhere isn’t working for this area of his face.

Is there something in particular that I can track down that he needs to be using to take care of this problem? A particular face wash or something like that which works well?