IME, anemones hide when they get stressed out. If they don't come out for a long time they will bleached and die due to lack of exposure to light.
What I normally do is, dig out the rock where it is attached to if I can, and relocate the nem where it is at least have exposure to light but not directly under a bright light. Blowing the nem with a turkey baster also helps relocating the animal.
Hope that helps.
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