If your pot of chives is big enough that you can get your hand around the clump, I would put on a pair of garden gloves and pull the chives out of the pot, roots and all, shake it off and replant in a clean pot.
Or you can cut off all your chives, put them in the freezer.
Fire ants are almost impossible to kill without a strong pesticide.
Most of the time all you can do is relocate them.
Check your surroundings for more mounds, if you find anything that gets rid of them, treat everything.
Personally, I've never seen fire ants in a pot, always in the yard.
@nanny24