If you are on the screen where you are clicking “Flip” and trying to save – you are already looking at the templates. The + at the end of the name means that this note type was (likely) imported, but it might or might not be pretty much the same as the default “Basic (and reversed card)” note type.
If that note type already makes 2 cards, I’m not sure what you’re trying to change about it. Can you explain more about that?
The error is telling you that you’ve changed Card 2 to be identical to Card 1 on their fronts – you posted a front and back template.
To switch between the card types in that template editor, you use the dropdown at the top –