Hello my watch will not switch on the apple sighn keeps flashing I have tried to force restart

If you have tried to First force restart it

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.

and the issue is still not resolved then Contact Support.

Click here > Contact - Official Apple Support

or phone numbers 

Click here > Contact Apple for support and service - Apple Support