Unpair watch when phone is lost.
How do I unpair a watch when the paired phone is no longer available?
Apple Watch Series 5
User profile for user:
Community User
From a web browser,sign in to iCloud.com with your Apple ID.
Go to Find iPhone.
Click All Devices at the top of the screen.
Click your Apple Watch.
Click Erase [device]. Select Next until the device is erased.
Click Remove from Account.