Keep your Apple Watch and old iPhone close together
On the old iPhone, open the Watch app
Tap All Watches
Tap the info button next to your watch
Tap Unpair Apple Watch
Enter your Apple ID password if prompted
Wait for the watch to finish unpairing and creating a backup
Turn on your new iPhone and sign in
Make sure Bluetooth and Wi-Fi are turned on
Open the Watch app on the new iPhone
Tap Start Pairing
Hold the Apple Watch near the new iPhone
Follow the on-screen pairing steps
Choose Restore from Backup if prompted
Select the most recent backup
Enter your Apple ID password if required
Finish setup on the new iPhone
If Activation Lock appears, enter the Apple ID and password used on the watch
If needed, update watchOS and iOS before pairing
If the watch was erased, pair it as a new watch or restore from backup