How do I unpair my Apple Watch from my new iPhone when the app on my iPhone doesn’t allow me to unpair?

Here are two ways to unpair your watch if you no longer have the paired iPhone:

• See the 'How to erase your Apple Watch if you don't have your iPhone' section of:

Unpair and erase your Apple Watch - Apple Support

• With a web browser, go to: https://www.iCloud.com and sign in with your Apple ID. Open Find My iPhone and select All Devices (at the top). Then click your Apple Watch, select 'Erase Apple Watch', and select Next until the device is erased. Finally click "X" next to remove your Apple Watch.

Did you unpair your watch from your old iPhone? Here's how: Unpair and erase your Apple Watch - Apple Support

Hope this helps.