In a situation where your event is rescheduled or delayed, you may need to change the event start date. It is important to make this change prior to the original event date having passed.
Within Eventsforce, the event 'start date' cannot be changed once the date has passed. You will see the error below when attempting to change event dates which have passed:
Potential workarounds:
Create a copy of your event (any completed registrations will either need to register again or be registered by an admin)
Leave the old event dates and update all emails to reflect the proper date by replacing the 'EVENTDATE' tag with plain text (will prevent the 'Add to Outlook' options from working). Also be sure to disable the "Show day selection page" feature if used