Hi , my Apple Watch shows red “!” , could you guide what can be done

Whether this can be fixed at home depends on the age and OS if the Watch

The process is suitable for Watch series 3 or later, OS 8.5 Onwards and iOS15.4 onwards only 

https://www.youtube.com/watch?v=l3Y2TBTfHTI 

With older watch or OS make a genius bar appointment to have it recovered.  

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