By any event you can see three dots where you can see "Edit event" menu.
In the list where you can see all your events, active and past, you can edit each of them by clicking on "Edit event" button. You can edit active and past events.
You can only change an event image, event status and event description. If you want to change other data, rather delete that event and create a new one. You can create a past event too if you like.
Event status: Active (default), Cancelled, Postponed, Sold out.