How can I pair my Apple Watch to a new iPhone
Trying to sign back in to my Apple Watch with a new phone
[Re-Titled by Moderator]
iPad 2, iOS 9
Question marked as
Here's Apple's support article on pairing your Apple Watch to a new iPhone. There's a section on if you have your old iPhone and another section near the bottom that says how you can pair without your old iPhone.
How to pair your Apple Watch with a new iPhone - Apple Support
Here's also the page on how to unpair an Apple Watch from an iPhone. The bottom of the page shows how to unpair on your Apple Watch.
Unpair and erase your Apple Watch - Apple Support