Switch Old apple watch to new apple watch
How to migrate all the settings and data from my old serie 4 apple watch to my new serie 6 Apple Watch
Apple Watch
Question marked as
When you unpair your old Apple watch, a backup is automatically taken to your iPhone. You can then point to that backup when pairing with the new watch.
The backup is described more in detail here:
Back up your Apple Watch - Apple Support
So start from here:
Unpair and erase your Apple Watch - Apple Support