This feature is only available on PCVR.
If you play BoxVR through Steam on PC, you can add custom songs to your workout by taking the following steps:
Open BoxVR
Choose ‘My Workouts’
Create new playlist by tapping the ‘+’ in the top left corner (playlist will appear below the icon and will display 0 min)
Select the ‘+♫’ on the top right corner
Select the ‘Files’ button - this will open the files on your PC
Navigate to where the mp3 file is located
Tap on the desired song and wait for the page to close
The bottom right corner will display ‘Processing…’ in red - once that is finished the song will be displayed in the newly created playlist (this may take a few minutes depending the length of the song)
Tap ‘Play’
If you find that your songs aren't processing correctly, or you enter a workout to find the targets aren't appearing please take a look at this guide.
NB: This feature is not supported on BoxVR for Meta Rift, Go, or PSVR, or on FitXR for Quest.