These are the recommended steps to take in sequence to ensure Sleep Watch is successfully transitioned to a new Apple Watch:

1. Make sure your Old Apple Watch is unpaired from your iPhone:  Go to the ‘Watch’ App on your iPhone and make sure that the Old Apple Watch is Not shown. If the Old Apple Watch IS shown, Tap the name of the Old Apple Watch.  You will be directed to an 'Apple Watch' screen with the name of the Old Apple Watch listed with a yellow 'i' to the right.  Tap the yellow 'i', then Tap to 'Unpair Apple Watch' or follow the onscreen instructions to unpair.  Note: you may wish to backup your old Apple Watch before completing this step.
2. Make sure your New Apple Watch is paired to your iPhone: Go to the ‘Watch’ App on your iPhone and see if the New Apple Watch is shown.  If the New Apple Watch is not shown, follow the on-screen instructions to pair the New Apple Watch to your iPhone.
3. After pairing the New Apple Watch, make sure 'Sleep Watch App by Bodymatter' is installed on your New Apple Watch:  Open the ‘Watch’ app on your iPhone.  Scroll down to ‘Sleep Watch’ and select (tap it).  ‘Show App on Apple Watch’ setting must be enabled (turned on).
4. Open Sleep Watch App on your iPhone. If you see ‘Welcome to Sleep Watch’, complete all the set-up / on-boarding steps until you see the 'Today' view.
5. Keep the Sleep Watch App on the iPhone open to the 'Today' view. This triggers a sync to your New Apple Watch.
6. Open the Sleep Watch App on your New Apple Watch. If you see a ‘Setup Required’ screen, then force-touch (firmly press on the screen) to refresh.
7. You should now see a recent Sleep Report or a ‘No Sleep Data’ message. Either of these messages indicates that you have successfully setup your Sleep Watch using your New Apple Watch. 
8. Wear your New Apple Watch to sleep for at least 1 hour to see your personalized Sleep Report on either your Apple Watch or your iPhone through your Sleep Watch App.