Did you not read what I posted earlier?
"If you do not unpair your Apple Watch with your old phone, but then enter the Watch App on the new phone, it will pop up saying 'Your watch is paired with another phone, reset your watch to repair" (Something like that). Well once you get that pop-up it immediately makes a backup of your watch.
Now you go to Settings-General-Reset-Erase All Content and Settings on your watch. Once that is finished you go back to the Watch App on your iPhone and pair like usually. It will prompt you to restore from the backup it just created moments ago.
Edit:
I should note. That any health/activity data is not included in that backup, but the iCloud/Encrypted iTunes backup only. So you will lose that data. But you will retain app data, settings, app layout and so on."