Unfortunately there is no simple button to do just that yet, but you can doing by following a little procedure that is documented at the following link Re: How do you duplicate or copy a Map Journal?
This will works well for Map Journal, Map Series and Swipe/Spyglass. For Map Tour that would not work well as you also need to duplicate the webmap so the most simple is that you create a new Map Tour from the web map.
Thank you so much, Gregory! I found, though, that I did not have to change the URL. The duplicate Story Map already had the same appid URL as what was in the URL bar. It seems to have worked, though.
