If the Apple Watch has stopped responding,I suggest performing a force restart. Steps needed are found in the Apple Support article: Restart your Apple Watch - Apple Support
i.e. press and hold both the side button and Digital Crown for at least 10 seconds, then release both buttons when you see the Apple logo.
If you've completed that troubleshooting and the issue is still not resolved, Contact Support as this is a new item.
Click here > Contact - Official Apple Support
or phone numbers
Click here > Contact Apple for support and service - Apple Support