Is it a heater malfunction? This happened to me before so first thing probably get rid of the heat source. And then if it doesn't go down you can try to put a bunch of ice in a ziplock bag and float it to help cool down the water. If the anemone is still attached to something then there's still hope. Shriveled tentacles happen from time to time. Just watch it the minute it's detached then remove it because it's dead, but if not try to nurture it back to life.