you can lift it out and use a q tip with peroxide to wipe it off/treat just the growth parts not contacting the flesh. we do this on lots of lps, one of our threads has me doing the exact same thing to a bowerb lps coral
then, target feed the coral better than normal and sustain that for four mos I bet you can get the tissue back over/inflated with expanded tissue maybe to reverse the mass loss trend.