Clicking on a title within All Subscriptions gives you the option to clone subscriptions from another title into a new title.
From this page you can add a customer (1), clone subscribers FROM (2) another title (for example if you wanted to clone them FROM Nightwing into Batman (2016) because Dick Grayson had taken over the role of Batman again as he deserves to do), or clone subscribers from the title you are currently in, INTO another title (3)
For this we'll clone INTO another title.
Right now we're in Batman (2016), we currently have 11 subscribers, and we'd like to move these folks INTO Batman (2025).
We click "Clone Subscribers Into" (3), and a modal window pops up.
In this window we'll search (1) for a title, in this case Batman, and we'll look for Batman (2025). We clone subscribers (2).
If they're already on this list, they won't get doubled up.
There's Batman (2025) all up to date!