Make sure your iPhone has Bluetooth and Wi-Fi turned on
Keep your Apple Watch and iPhone close together
Open the Watch app on your iPhone
Tap All Watches
Tap Add Watch if your watch is not listed
If your watch is already listed, tap it and follow the on-screen steps
If prompted, enter your Apple ID and password
Restart both your iPhone and Apple Watch if they do not reconnect
On Apple Watch, press and hold the side button, then slide to power off
Turn both devices back on
If needed, unpair the Apple Watch from the Watch app
Set up the Apple Watch again and restore from backup if available
If the watch still will not reconnect, reset network settings on your iPhone
If the issue continues, contact Apple Support