How to add instrumental (back music):
1- Go in the Event sheet
2- Click "Add event"
3- Click "System"
4- Under "Start & end" choose "On start of layout"
5- Click "Audio"
6- In the Add Action box that appears, under General click "Play"
7- In the "Parameters for Audio: Play" box that appears, choose the file in the Audio file drop-down menu.
8- in the "Loop" drop-down menu choose "Looping"
9- Click the "Done" button.