Complex sentence: Requests are listed on the open tasks list under "unassigned" cases; when a mediator reviews a case and decides to take on the mediation, he or she moves the case listing to "assigned" cases and contacts the parties.
Split into simpler sentences: Requests are listed on the open tasks list under "unassigned" cases. A mediator who reviews a case and decides to take on the mediation moves the case listing to "assigned" cases and contacts the parties.