How can I unpair my watch to an iPhone I do not have any longer? I have a new iPhone

See How to pair your Apple Watch with a new iPhone

Click on If you don't have your old iPhone

On a computer, go to iCloud.com and sign in with your Apple ID.

Go to Find Iphone.

Select All Devices, then click your Apple Watch.

Click Erase Apple Watch.

Select Next until the device is erased.

Click the remove button next to your Apple Watch.

I purchased a new iphone and before I start the transfer it tell me to unpair my watch...How?