I am still not understanding. Take the power head out and scrub it off. While an aiptasia can regrow from tissue, it is not going to replicate itself from a single cell or spawn millions of babies if you miss a piece and it does regrow. It is not rooted in the plastic or immortal. If it were to regrow because you missed a bit it’s not going to take over the tank in a day. Just scrub the power head off. Use some bleach or peroxide if you wish or just use hot water. Use soap if you want.
12% peroxide can be hard on some plastics and synthetic rubber materials. The PH could be pvc, abs, styrene, etc. who knows. You can find a table for reactivity if you know the plastic.