I'd recommend using something like Joe's Juice, Chem Marin Stop Aptasia or Red Sea Aiptasia X.
It may take a couple applications but it will kill it, eventually.......
If you try to scrape it off, make sure you take the rock out of your tank. Often times little bits of scraping float away and regenerate.
You can also try peppermint shrimp and sometimes a copper banded butterfly. Unfortunately these are hit and miss remedies with mojanos.
Good luck!