Definitely not a bristle worm WOW! Nice picture nothing left to do, it's dead.
As for picking them out with tweezers, good luck with that! Only time you can do that with any success is if they are completely and I mean totally out of the rock. These lil buggers are strong and will break before giving up their grip. Chances are after your fresh water soak most if not everything once living in the rock has now perished. The good and the bad. Your rock will now begin to smell like a compost pile, well maybe worse then that, yea I remember it's a lot worse lol. So now your going to have to continue to clean the rock. Or if it were me? Dump it all and buy new