You can use the Remote app on Apple Watch to play music in iTunes on a computer on the same WiFi network.
Add an iTunes library. Open the Remote app on Apple Watch, then tap Add Device. In iTunes on your computer, click the Remote button near the top of the iTunes window, then enter the 4-digit code displayed on Apple Watch.
Don’t look for the Remote button in iTunes before you tap Add Device on Apple Watch—the button appears only when a remote is trying to connect. In iTunes 12 and later, the Remote button is in the upper left, below the Volume slider. In iTunes 11 and earlier, the Remote button is in the upper right, below the Search field.
Choose a library to play from. If you have only one library, you should be good to go. If you’ve added more than one library, tap the one you want when you open Remote on Apple Watch. If you’re already playing music, tap the Back button in the upper left of the playback controls, then tap the library.
Control playback. Use the playback controls in the Remote app. Turn the Digital Crown to adjust volume.
Remove a library. In the Remote app on Apple Watch, tap the Back button in the upper left to view your devices, firmly press the display, then tap Edit. When the device icons jiggle, tap X on the one you want to remove, then tap Remove. If that was your only remote device, you’re finished—otherwise, tap the checkmark to finish editing.