Occurrence or Series Dialog

The event you are asking to edit is a Recurring Event. When you edit a Recurring Event, you have the choice to edit a specific occurrence of the recurring event, the occurrence and all future events, or the whole series (past and future) of events.

For example, you have a Group that meets every Thursday at 7:00 PM, but next week you will be meeting a little early. You can choose to edit the occurrence and change the time for that one meeting.

When you edit an occurrence, an exception date is created for the original event and a copy of the event is created as a one-time event.