its not working

Put it on charge for 1 hour, then try to force restart the Watch

ie hold the digital crown and the side button in together until the Apple Logo appears.

If forced restart does nothing then reach out to Apple Support

You should be able to reach them here

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

Restore your iPhone: If the above steps don't work, you may need to restore your iPhone using iTunes. Connect your iPhone to a computer and open iTunes. Follow the on-screen instructions to restore your iPhone to its factory settings.

Or put it on charger for some time (if possible, to an original one, as well as a cable) and try again.

DFU mode, but it would be useless if iPhone does not respond to anything.