If it is extremely bad, consider clipping the end of the tentacle. The tentacle tip would die regardless, if it continued to have a large bubble trapped in it.
I have seen this happen on rare occasion when a weak/stressed anemone is kept in a holding tank with a venturi or lots of bubbles. Note that in the wild anemones can often live in/close to the surf zone so they have the natural ability to block bubbles or eject them. However if they are weak, you may need to step in. Anemones can lose tentacle tips without much harm to the entire anemone. People report all the time when their aggressive clowns will rip off tentacle tips, or sometimes even entire tentacles.