Because it is still on a plug, remove the coral to a separate bowl filled with tank water. I would use a syringe with boiling water to then cook it where it sits. If you try to just scrape it off, any small fragment will just regrow. That is also the problem with doing that in the main tank. The last thing you want to do is help it spread!
The other option is to just remove your coral frag from the plug and toss the plug. Either place it in it's forever home or on to another plug (or small piece of rock), whichever works best for you. A couple drops of superglue gel and you're set to go.