From what I've read, there are drills that can help QBs improve their arm strenth. The problem is that it doesn't appear to be a "quick fix" issue. Also, given the NCAA rules about the amount of time coaches/trainers are allowed to spend with players during the offseason, the player really has to commit to wanting to improve his arm strength on his own.
The insane arm strength Pat Mahomes has he started working on as a kid with his Dad. It isn't something he started working on at TTU. Interestingly, he and other pro QBs known for their arm strength credit playing baseball, and baseball drills, for helping develop their arm strength.
On a handful of passing attempts each game, Patrick Mahomes seemingly shreds the laws of physics.
www.stack.com