If you want to pair your apple watch to new iPhone 7 or iPhone 7 Plus, then you’ll have to unpair your Apple watch With iPhone. The reason for this is that you can only Pair your Apple watch with only one iPhone at any one time. So, every time you want to change your old iPhone to new iPhone 7 or iPhone 7 Plus, you have to Erase content from apple watch or Reset apple Apple watch and unpair Apple watch from your iPhone. Note: Resetting Apple watch also Unpair’s apple watch from iPhone and un-pairing the Apple Watch creates a backup that’s stored on your iPhone. And, if you Un-pair your Apple watch from iPhone by resetting your Apple Watch directly, then it will not create a backup. If you need or want a backup, make sure you unpair using the Apple Watch app on your iPhone.
How to unpair Apple Watch from your iPhone using the Apple Watch app
STEP #1: In the first step, Just Open up Apple Watch app on your iPhone 7 or iPhone 7 Plus.
STEP #2: Then, Click on Apple Watch which is under the My Watch tab.
STEP #3: Now you have to Tap on Unpair Apple Watch.
STEP #4: Tap Unpair again to confirm that you want to Unpair Apple Watch from iPhone
STEP #5: You may have to Enter passcode
Apple Watch will make a backup and Will be reset.
How to unpair Apple Watch without iPhone and Erase content from apple watch
STEP #1: Go to Settings app on your Apple Watch.
STEP #2: Then Go to > General settings.
STEP #3: Now, Tap on Reset.
STEP #4: Just select Erase All Content and Settings.
STEP #5: You may have to enter your Apple watch passcode.
STEP #6: Tap on Continue to confirm the reset.