Changes the raid or dungeon instance for the selected event. Only applicable if the event's eventType is set to 1 or 2 (see CalendarEventSetType).

A list of dungeon or raid instances can be found by calling CalendarEventGetTextures with the current eventType. That function returns three values (name, icon, and expansion) for each instance in the list; e.g. to get the index for use with this function, find the index of the instance's name in that list and divide by 3.