Educate. My partner used to be against me breastfeeding in public because he's overprotective. What I did is I added him in Breastfeeding Pinays so he will be part of the growing people who normalize breastfeeding in public. Now he allows me, but he still asks me to cover. Little by little, I know we're getting there.
I agree with Mikaela. Educate him. Make him watch videos, make him read articles, make him a ppt (kidding) lol. But yes. You should make understand why he should support you and let him know why it would be beneficial to both of you :)