Lama Ole’s answer:
If he is willing to say a mantra, then a few million repetitions of OM MANI PEME HUNG would be good. That removes a lot of aggression.
I myself lost interest in fighting during my first visit to a nude sauna. There I suddenly saw how much naked skin there is that can be injured, how vulnerable people really are. When I left the sauna I thought, “Now I will protect them. Now I won’t beat them up anymore; I will change the program.” And that was very good!