Go to Menu → Calendar Events → Search Calendar Events and find the event you want to copy.
You can either click the dropdown to do an advanced search…
… or click the red x next to any automatically applied filters to open up your search results.
Click anywhere on the row of the calendar entry you want to copy to open it. In the top right corner, click Actions, then click Copy Calendar Event:
A modal will open – set the new date/s for the event, then click Save:
If you need to make further changes to the details of the event in either the Event Information and/or Event Attendance, click Edit, change the details as required, then click Save (which will become available once you have modified any of the details).
Once the details are up to date for the new event, you need to add the participants (these are not copied) to the new event. Information on this can be found in Adding Community Members to a Calendar Event.
When the event has all of the correct details, and has the participants attached, the event is ready to activate. Information on this can be found in Activating an Event.