Best way to introduce a head collar

I have been advised to use a head collar for Harry. The advice was to use a Halti, and if I found his muzzle was too short for it, to try a Gentle Leader. I have ordered a Halti from Amazon today for delivery tomorrow and would welcome advice as to the best way to get my boy to accept it please as Ive never used one before. I don't imagine its going to be easy

the same way you do a muzzle, just gradually introduce it, for example put it on the floor and some treats init, and then half put it on again with treats, and then fully on and then leave it on for a while before you go for a walk.

the stages may take more then one go aswell as some dogs really do not tolerate them to begin with

Great advice from Ella above cannot really anything else.