my apple watch was paired to my old iphone how do i connect to my new one

Erase it before pairing it to your new phone

If you don’t have its paired iPhone, erase your Apple Watch 

If you can't unpair Apple Watch because you don't have its paired iPhone, you can erase the watch.

When you erase Apple Watch instead of unpairing it, the watch is still protected by Activation Lock. Before you can pair Apple Watch again, enter the Apple ID and password that was used to set it up.

1. Open the Settings app on your watch, then tap General > Reset.
2. Tap Erase All Content and Settings, then tap again to confirm.
3. Wait for the watch to unpair.
4. After Apple Watch unpairs completely, you can pair again. You'll need the Apple ID and password that were used to set up the watch.

Pay attention to the section in this link about "If you don't have your old iPhone" --> How to pair your Apple Watch with a new iPhone - Apple Support