Boxing lessons is always a good answer when people ask to improve their stand-up as most Boxing gyms are legit unlike some MT ones where alot of McDojo's have popped up recently. I know first hand
. But if this guy is saying all he does is punch then maybe a decent Muay Thai gym would widen his arsenal and if he's primarily a ground fighter then more deverse strikes might benefit him keeping the opponent off guard before rushing in for a takedown. If he wants to be a striker then good hands are important but like has been said we need more information.