If I understand correctly, you have disconnected the plastic screening tube from the powerhead. That plastic piece is still on the tentacles, but there is no water movement dragging the anemonee into the pump? If this is the case, I would just leave the anemonee alone and let him withdraw from the plastic part by himself. If there is no water flow continuing to pull him in, he should be able to get out at his own pace. If he is still entangled tomorrow (which is very unlikely) then I would suggest slowly and gently pulling it off.