How do I unpair my apple watch when the phone that is paired does not work?

Unpair and erase your Apple Watch - Apple Support

Se the 2nd procedure;

How to erase your Apple Watch if you don't have your iPhone

M1 Mac mini, macOS 12.4; Watch, series 5 GPS/cellular, watchOS 8.6; iPad Pro 2nd Gen, iPadOS 15.5; iPhone 12 Pro, iOS 15.5; TV 4th Gen, tvOS 15.5; HomePods, audioOS 15.5 and Airport Express w/ Airplay 2

To unpair and erase watch and remove Activation Lock

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.