B.W.
I assume you HAVE to wean him for some reason. If you don't have to, then self-directed is always easiest. Waiting until they know how to use a cup and can drink cow's milk. All mine did it between 11-15 months. It was easy and not tramatic for either of us. But if you have to, then you need to get him used to the bottle using expressed breast milk first. HE won't like the taste of formula, that's pretty normal. It tastes nothing like breastmilk, which is sweet. It is not sweet, has a distinct odor and taste and can be a little grainy if not completely dissolved. So, it is an adjustment for a baby used to breastmilk. So start with pumped breastmilk in the bottle. It also helps having someone else be the one to give it to him. And you can't be around. If you are he will want you. If you can get him drinking that from a bottle or cup, whatever, then start mixing breastmilk with formula, making the percentage of formula just a bit more each time. That way he slowly adjusts to the different taste. He should eventually get used to it. He will take it eventually if he has to though. He'll simply get hungry enough that he won't care anymore....