You can duplicate a Campaign from your Back Office.
To do so, click on the campaign you'd wish to duplicate. Then click on the three blue dots box (between the status of the Campaign and the Save button).
You will find an option "Duplicate". Click on it. That's it, you will be automatically directed to the copy (remove the "(copy)" from the title)!
You can change the start date but do not change the end date manually: it will change automatically
Lastly, do not forget to activate it!