Swipe up from the bottom of the screen to reveal your Control Center. From there you can play, pause and skip songs. You can also enable AirPlay or change the system volume.
Similarly on Android, launch your music player outside of BitGym. Then after switching to BitGym, you should be able to swipe down from the top to reveal the Android status bar. Pull this down and you can play/pause/skip your music.
Warning: Many Android devices have low memory and can crash when trying to use BitGym together with a music player. Use with caution over longer workouts as it may result in the app crashing and your workout being interrupted and not saved to your history.
Coached music: Unfortunately the music for coached workouts is baked in with the coaching voice and this is the format in which we have the rights to distribute this content. Hence the music cannot be independently muted. To play your own music you will have to mute the entire coaching - voice and music both.