Thanks y'all! I will try those!
Associate it with treats/whatever you give them. Give them treats then show them the bottle. Horses are smart so you don't have to do it very much. Apply it and than treat and then apply then treat etc. but then eventually you can do one hoof then two treats or something like that
Maybe you could show him the bottle and leg him sniff it
Maybe have someone lift on of his front legs so he can't kick out easily as you do the other ones? Also maybe regularly put on hoof grease or oil so he becomes very used to the reigeme?