Hey Stefanie,
Thanks for reaching out.
This was never a feature of our plugins—you were probably able to do this by way of using an unofficial plugin called “Event Rocket” that added features like this to The Events Calendar.
That plugin is no longer maintained and so it’s unfortunately not possible to use that plugin for these features any more.
I don’t know of any alternative plugin that provides that feature, so unfortunately it is not possible to “duplicate” or “copy” events at this time.
Sorry to disappoint! Please let me know if there are any other issues or questions I can try to help with.
— George