Go slow. Feed him a lot
of treats while he has it on, or better yet,
use an activity treat.
In other words, play a game that he loves or take him someplace that he loves, but only with the muzzle on. If he learns to associate the muzzle with good things, it won't be stressful for him when you get it out and put it on him. If he fusses and wants the muzzle off, get him calm before you take it off, even if he's only momentarily calm. Pick your moment, when removing it.