Start by going into Manager and then simply:
Find the campaign you want to duplicate
Click on the little two squares next to the campaign name (..as shown below in the image)
Then choose the campaign section you want the campaign to be added to
....And then you're done 🎉
When you have duplicated the campaign you of course have the option to change the name - see this article on how ✍🏼
Happy duplicating 😄