It really depends on what you are looking for. Many people just leave them to their natural habit which is to reproduce side by side into a "mat." If you are ever concerned about vigor you can cut back selected plants. Eventually it will get crowded and probably need divided. Like any spreading plant every few years you could dig up the whole bunch and split them. Pot up some pups and just replant a couple to settle back in.

As for just removing the small one out of the center that would be a nice trick, I'd like to see it. J/K. The larger plants that came from the original corm have likely grown apart and would just have tangled roots. The smaller pup is still going to be attached fairly deeply to one of the bigger plants. Besides guessing where that connection is I don't think you have room to get in there with any tool without damaging a lot of other material.

Probably getting too late this year to split them so if you experience die back, I would wait till signs of growth next spring, then dig and separate. Kind of like splitting a bed of bulbs.