Bristle worm traps work pretty well, there are several DIY designs out there that can usually be made out of stuff on hand. There are also a couple traps sold commercially.
Chances are there are more than just the one in the tank, while they do a lot of good for the tank through detritus and left over food consumption, they can be a real nuisance if their population isn't controlled. I recommend finding a natural predator that will get a long with your tank inhabitants. For comedy, Coral Banded Shrimp are good and are coral safe ( I have seen one grab a worm, rip it in half and double fist eat it - made for quite a good laugh) and Arrow Crabs can do the same but are definitely cautioned around polyp corals especially zoas. I have some people also recommend a variety of wrasses, with Six Line wrasses being a usual suggestion.
At 3" I think your worm would be too big for any of these options so I would start with a trap and then add a control option.