What should I do if my 6 month baby does not want to drink any form of formula?

Transition slowly. Breast milk tastes radically different from formula, and babies get used to what they have been on. I'm assuming that you pump and feed with a bottle, and if not, start. You can start by adding 3/4 breast milk and 1/4 formula to a bottle and starting that for a week or so. Then slowly transitioning to 1/2 of each, and eventually working breast milk out of the bottle entirely.
Try a Cup. In your comment, you mentioned bottle difficulty. Why not go straight to cup. No reason not to.