To create a new set, switch to the sets menu and make sure you are on the ‘All Sets’ page, if not use the back button at the top of the menu to navigate back to it. From the ‘All Sets’ page, you can create a new set using the add button at the bottom of the menu and can (optionally) give the set a title, and date.
To edit the details of a set, open the set and press the edit button edit at the top of the screen. From here, you can edit the name or date of the setlist.
Setlists are ordered in your library by the date assigned to them, so editing the date on sets will change the order they are displayed in.