[Zubersoft]

Sorting by date created with descending sort order (so the most recently created song is at the top) is the easiest way to select all of the duplicate songs and delete them. If you want to delete from the setlists, collections or any group tab, while viewing the songs inside the group, long press to start selection mode, select each song to delete, tap the three dots at the top right and then select "Delete Song from Library". That will permanently delete the song (which is the same as deleting from the Songs tab). There is a separate "Remove" action, but as Geoff said, that just removes the song from the setlist. It's set up this way to prevent users from accidentally deleting songs that they just wanted to remove.

Mike