How can I pair my watch if I don’t have access to my old phone?

Need more help?

1. Erase your Apple Watch.
2. Set up your new iPhone and sign in to iCloud. ... 
3. Open the Apple Watch app on your new iPhone, then pair your watch with your new iPhone.
4. Try to restore from a backup. ... 
5. Follow the onscreen steps to finish setting up.
6. Start using your Apple Watch with your new iPhone.

How to pair your Apple Watch with a new iPhone - Apple ...

This;

Request online activation lock removal.

Or this;

If you can't remember/gain access to the apple id that paired the watch to the phone.Take the watch and it's receipt along with some photo id and any other proof of ownership to an Apple Store and request that they remove the Activation Lock for you.

Otherwise the watch will be of no use to you.

About Activation Lock on your Apple Watch - Apple Support