To edit an existing schedule exception, open the Schedule Exceptions window (Administration-->Side menu-->Scheduling-->Exceptions)
Choose the type of schedule exception you would like to edit (Clinic Exceptions, Workplace Exceptions, or Resource Exceptions).
In the area below the filters you'll see a list of all current exceptions.
Click anywhere on the exception you would like to edit. This will open the Edit Scheduling Exception pop up window. From here you can make needed changes to the scheduling exception.