[Delphinus]

Agreed with Brad. Try some of that, or some shrimp or prawn (1/4" pieces approx should be OK) or some mysis. I've had a modicum of success reviving stressed-out looking anemones using a high protein food like mysis, the trick to to make sure they're actually eating it.

How is water flow over the anemone right now? Thing is they can sometimes shy away from a direct powerhead kind of flow but they really do need a fair amount of water flow. O2 saturation is important for them and too much CO2 can make them do weird things too. There should be
enough current to keep the tentacles gently swaying constantly. If you find that food drifts off the tentacles when you feed, you may need to turn your current off for 5-10 minutes when you try to feed it. Also watch out for any kind of tankmates that might steal food, cleaner shrimp, peppermint shrimp can be really pesky that way sometimes (despite target feeding, the animal gets pretty much all it food stolen).

You can try flipping the rock over but bear in mind it will want to have that foot in a crevasse or under an overhang or something. If you can rearrange the rock such that it is still underneath it, but if it could "reach" out into the light, that might be something workable.

You don't have any other anemones in the tank do you? They can sometimes interact negatively with one another.

Unfortunately, there is the one sad possibility that whatever's happened to it along the way has stressed it too much. A lot of anemones don't make it past the first month to couple of months due to injury, infection, starvation or other stressors that may have happened well before it ever got purchased to go home. They have slow metabolisms so it can be a while before a declining health can be obvious. That said, as long as something isn't too far gone they can recover from a great deal more than we give them credit for. But with THAT said, you should be aware that the statistics are unfortunately not exactly 100% -- you can do everything by the book and still be disappointed and you can do everything "wrong" and still get lucky so at this point it can probably go either way.

Another possibility is that it is going through a light shock if the lighting is significantly different in its new tank from its last tank. In which case letting it hide under a rock (provided it can still get water current, and food) is probably best and it will come out in its own time. Of course, it shouldn't be so withdrawn into the rock that it gets no light whatsoever, but if it's only under a ledge or something that's probably not a huge concern in and of itself.