The following steps will allow you to make a copy (clone) of an event.
If the event is a single occurrence in the past, use the filter on the Events page of your site to search for it. If the event is a recurrence master and you'd like to make a copy of the master, navigate to Recurrence Masters and find the master you'd like to copy.
For a single event: click on the name of the event to open it, click the ellipsis button in the upper right, and choose Save Copy of Event.
For a Recurrence Master, click the ellipsis button and choose Save Copy of Master.
You may now click Edit to change the Event Name, Start/End Date/Time (if a single event) or any other details you'd like the new event to use.
Click the Save button a the top to save your changes. If you are saving a copy of a master, you should automatically be taken to the Instances page of the new master.