If you can reach it, you could turn off your pumps and try to gently remove it from the overflow and place it back into your display. If it's attached, there are a few folks here who've posted some tips/tricks for getting them to release. High flow directed at the foot, ice cubes, using a credit card to gently pry the foot loose, etc. Other than that, I'm not sure what to suggest. The 1 anenome that I tried to keep was very fond of the PH's, so.... it didn't make it long.
Sorry that I can't be more help... maybe someone else will chime in.