Hi
It may help to restart both your iPhone and your watch:
- Turn both devices off together first, then restart your iPhone before restarting your watch:
- To turn your watch off: press and hold the side button until you see the Power Off slider; drag it to turn off;
- To turn it on: press and hold the side button until you see the Apple logo.
Otherwise, it may help to unpair and re-pair your watch:
- The Watch app on your iPhone takes watch backups automatically, including a fresh one when unpairing via the app.
- Choose to restore your watch (Restore from Backup) when offered the option during set up. Most data and settings will be restored, with some exceptions (eg Apple Pay cards, passcode).
- Unpair your Apple Watch and iPhone - Apple Support
- Set up your Apple Watch - Apple Support