How to Use Interval with Offline Music
#1. APPLE MUSIC
#2. SPOTIFY Premium
Select the options on the bottom right - a device where you want to play the music. You should select Apple Watch as the option. (below)
TIP: You might want to turn off the Apple Watch passcode and wrist present sensor to make it more user friendly.
TIP: Make sure to activate watch lock to avoid the screen buttons getting pressed accidentally by water droplet.