Exactly how to do this varies on the situation and venue.
You can briefly stop the match to consult with either the host administrator or the home coach, depending on the venue and situation. It's best to do this between sets or during a regular timeout, if possible.
If the coach provided the LJ (and he/she is complaining), it may also be worthwhile to ask them what they suggest about the LJ problem. They may be able to resolve it by telling the LJ to pay attention (if that is the problem), or they may say that they can replace with someone good.
Bottom line: The host admin or coach should be the one to make the replacement at your request. If they refuse or don't have a suitable replacement, you have even more of a situation on your hands.
