How to stop the ring tone on the watch and vibrate only
Welcome to iMore! The easiest way is to swipe up from your watch face, switch to the Settings glance, and tap the silent button.
You can also open the Watch app on your connected iPhone, then go to Sounds & Haptics and activate Silent Mode.
A third method: Using your Watch, go to Settings > Sounds & Haptics, then activate the Mute toggle.