Before thinking how to get rid of them, consider that they will act as part of your system’s clean up crew. They’ll eat any leftover food, detritus or dead creatures that you may have. In the unfortunate event of a fish dying, you’d probably remove it, but if a snail dies behind a rock, you need something to clean up after your clean up crew. If your tank seems to have a lot of them, it’s likely a symptom that there’s too much decaying organic matter that typically comes from overfeeding.
Once you address that issue, the bristle worm amount will level out. You can remove them if you like, but don’t touch them with bare hands as those hairy looking edges will irritate your skin. If you think that you don’t have any and maybe should add some, don’t bother because they’re probably already there!