You can play audio from Apple Watch on Bluetooth headphones or speakers.
Tip: If you have AirPods that you set up with your iPhone, they’re ready to use with your Apple Watch—just press play.
Follow the instructions that came with the headphones or speakers to put them in discovery mode. When the Bluetooth device is ready, follow these steps:
Go to the Settings app on your Apple Watch.
Go to Sounds & Haptics > Headphone Safety, then tap Reduce Loud Sounds.
Turn on Reduce Loud Sounds, then set a level.
If you listen to loud audio through your headphones for long enough that it could affect your hearing, Apple Watch sends you a headphone notification and automatically turns down the volume to a more moderate level to protect your hearing.
To view details about headphone notifications, follow these steps:
Go to the Settings app Choose an audio destination on Apple Watch