If your Apple Watch is lost or stolen
If your Apple Watch is missing, the Find My app can help you find it and protect your information.
Here's how it works
Find My can help you locate and protect your missing Apple Watch. If you already set up Find My on your paired iPhone, it's automatically set up on your Apple Watch and any Apple Watch that was paired using Apple Watch For Your Kids. And with Activation Lock, your Apple Account and password are required before anyone can erase your Apple Watch and use it with their iPhone.
Put your Apple Watch in Lost Mode
If your Apple Watch goes missing, you can immediately lock it using Lost Mode from your paired iPhone or iCloud.com/find. Then you can send a custom message that will appear your watch so that if someone finds it, they know how to contact you.
On your device
Open Find My, tap Devices, then select your Apple Watch.
Tap next to your watch's name.
Under Lost Apple Watch, tap Lost Mode.

Tap Continue.
Enter a phone number where you can be reached, then tap Next.