Existing Apple Watch will not pair with new iPhone 13 Pro

Remove the watch from your old phone first;

From a web browser,sign in to iCloud.com with your Apple ID.

Go to Find iPhone.

Click All Devices at the top of the screen.

Click your Apple Watch.

Click Erase [device]. Select Next until the device is erased.

Click Remove from Account.

Then go here;

How to pair your Apple Watch with a new iPhone

First off all, if that  WATCH it’s already activate your have to restore within the Apple Watch settings then use watch app on your iPhone to pair it follow the steps and let it finish leave boths iPhone and watch closer

When I go to Find My iphone, my watch is not listed - I cannot get it to pair with my new 13 pro max. I traded in my old iphone at T- Mobile but an offline iphone still shows on Find My iphone. Should I remove it? Also having issues with my Airpods staying connected on my 13 pro max.

My problem is I erased my old phone before I unpaired my watch. Now what?

Ssme. T-Mobile transferred and took old phone and never mentioned anything about bathe watch or AirPods or keychain disappearing.