How to open up the overflow drain cover of a massage bathtub?
Contact American Standard. I've seen images online that show they have tubs with this type of overflow. They should be able to advise you.
Also it looks as if you don't have any caulking around the edge of the tile joining the bathtub. It would be a really good idea to run some silicone caulking around that edge. Make sure it's silicone and you can get it in clear. If you're not used to using silicone it can be kind of messy when using it.