There is currently no way to "restart" you event once it has ended.
Once your event has ended, it goes into the "completed" state and cannot be restarted. The reason for this is to maintain proper analytic reports based on a start and end time. While in completed state, you can view analytics and view all the posts from the event.
We do plan to add functionality in the future that would help for reasons of why you would want to restart an event. A couple of those functionalities would be:
Duplicate Event: You want to start the same event because you want all the same event settings (same hashtag, footer, etc.) and not have to "redo" all the settings again. With duplicating the event, all event settings would be automatically populated, but would run as a separate event.
Load Posts from Other Events: You are running a display and you want to add in all the posts from another event into a new event.
** Both these features are on our radar and will hopefully be a solution to why you would like to "Restart" your event. If you have another reason or potential feature in mind for why you would like to "Restart" your event, please email us at email@example.com.