How do i pair my old Apple Watch to my new iPhone if I don’t have my old iphone

To unpair and erase watch and remove Activation Lock.

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.

Then go here;

Pair the watch with my new phone.

In addition to what fireyjack said, you can also try the steps in the 'How to erase your Apple Watch if you don't have your iPhone' section of:

Unpair and erase your Apple Watch - Apple Support

if you find that easier.