ChanServ maintains a list of rooms that you have identified to. The unidentify command allows you to remove an entry from that list, effectively making ChanServ unaware of the fact that you have identified to a specified room.
Example:
/msg chanserv UNIDENTIFY #support
If you needed to identify to take care of something, but do not normally have founder access, you may wish to unidentify. You also might want to unidentify if you want to enter the room without being given operator status automatically in the room.