eh sounds like a bad idea to introduce a predator....majano wands will work on polyps and soft corals, you can also try taking a syringe and inject it with aipstasia x or lemon juice or something
How much rock did they cover? It might be easier to just give away, or sell the rock they are attached to. Introducing a predator is not a good idea, killing them in tank is not such a great idea either as they can poison you and make you seriously, seriously ill.
get it out of your tank - you can zap them or have something eat them, but the predator you likely put in will eat them LAST and everything else first and zapping them will take forever and you'll need to make sure you keep an eye on your stability
Like house said I would remove from the tank. Just let the rock soak in a bucket with plain RO water. They'll die with lack of salinity. Once they're dead remove the rock using latex gloves, discard the water in the toilet and rinse the bucket with COLD water and vinegar.
Only the use of HOT water is dangerous since the palytoxin they may excrete would go airborne in the steam. If you use cold water for each step you'll be fine.