How can I get my old data from my Apple Watch back
How can I get all my workouts back onto my Apple Watch, I upgraded my phone and it seems it is all gone :(
iPhone 12 Pro, iOS 14
Here is how to transfer your Apple Watch from your old iPhone to your new one:
How to pair your Apple Watch with a new iPhone - Apple Support
The steps to follow depend on whether or not you still have your old iPhone.