Restoring, or importing any iReal Pro file, is just opening it with iReal Pro, whether the file holds one song, one playlist, or a whole backup.

 

On iPhone and iPad, tap the file in Mail or Files, tap Share, and choose iReal Pro. On Android, tap the file and Open with iReal Pro. On Mac and Windows, open it with iReal Pro or drag it onto the app.

 

For more, see Back up and restore your library on the iReal Pro website.