Watch frozen, unresponsive, flashing, spinning or steady Apple logo
I suggest performing a forced 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.
Click here > Contact - Official Apple Support or phone numbers Click here > Contact Apple for support and service - Apple Support and or Genius Bar Reservation and Apple Support Options - Apple