Get a golfball, lacrosse ball, or water bottle filled with SOLID ice. Then press the front of your heels into it, and vigorously massage the painful parts of your arches with these. This will stretch out the fascia muscles, because fasciitis is a form of contracture. It will be sore at first.
If you have pain in your heels specifically, it might be heel spurs on top of the fasciitis. In that case, get some insoles specifically for heel spurs. Esp. if you're on your feet all day, because that's how heel spurs form; repeated impact. In that case, you should also just ice your feet at the end of the day with some icepacks.
I recommend these insoles for heel spurs.
If your feet are sore in general, and you're on them all day, the secret is to keep moving. Standing still makes them more sore, as counterintuitive as that sounds.
