Apple logo just flashes while on charger

Then you will need to contact Apple Support directly for assistance.

World-wide Apple Support -

https://support.apple.com/en-us/HT204169

Support by phone, email or chat -

https://getsupport.apple.com/

Apple Support by Twitter -

https://twitter.com/AppleSupport

ASC - Late 2012 Mac mini, macOS 10.14.6; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.6.1; iPhone 8+, iOS 13.6.1; TV 4th Gen, tvOS 13.4.8;  HomePods, audioOS 13.4.8 and Airport Express w/ Airplay 2

ASC - Late 2012 Mac mini, macOS 10.14.6; Watch, series 5 GPS/cellular, watchOS 6.2; iPad Air 2, ipadOS 13.6.1; iPhone 8+, iOS 13.6.1; TV 4th Gen, tvOS 13.4.8;  HomePods, audioOS 13.4.8 and Airport Express w/ Airplay 2

Have done this multiple times. I even factory reset the whole watch and set it up as a brand new watch. It worked for a single day and then it stopped working again!

It will sometimes boot up and let me put my password in, then it will start to restart again!