I don't have flat feet but my ankles turn inward when I walk so I end up putting a lot of pressure on the inside of my arches. I used to get really bad bruising and soreness when I worked in food service, even when I just worked a four hour shift. I used shoes inserts that offered support to the inner arch as well as padded the heels and balls of my feet, and that definitely reduced pain but not by much. Management just needs to learn to be okay with their employees sitting while working imo

I had similar foot pain when I started my summer job last year (I'm also a bit flat footed and have been told that I walk weird too which made be a bit self-conscious about how I walk). The way that I helped to alleviate the pain was by getting insoles to help support the arches of my feet, which is supposed to help you to stop walking on the inside of the feet. Now while I went to a foot doctor to get the exacts of it all and a specific brand, not everyone can do that, but I know in some places like Walmart you can get more generic styles of insoles and do a quick foot measure to see what type of insoles you need. (Just make sure your work shoes have the ability to remove and replace the insoles that are already there)

If you lay on your back and rest your legs straight up, it will help with a lot of the pain and the swelling. You need to do this for a while though and make it a habit. I learned from my mom (a teacher) and an old friend (ER nurse).

It's hard but when I have the chance to stand still I like roll my balance from my heels to my toes and it like makes me perfectly balanced and I try to walk like that. I walk more on my heels and lean on my pinkie toe.