Apple Watch ISO update`

Watch frozen, unresponsive, flashing, spinning or steady  logo 

If the Apple Watch has stopped responding,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 > https://support.apple.com/en-us/HT201232 

The rest of the advice was contact Apple.

However try the steps here to troubleshoot not being able to update: Update your Apple Watch - Apple Support 

Need more help with updating? 

Try these steps: 

Make sure that your Apple Watch is connecting properly to its charger.  

If your Apple Watch won't charge or won't turn on – Apple Support (UK)

 Restart your Apple Watch – Apple Support (UK)

 Restart your iPhone – Apple Support (UK)

Try again to update your Apple Watch. 

If the update won't start: 

Open the Apple Watch app on your iPhone. 

Tap General > Software Update. 

Delete the update file. 

Try again to update your Apple Watch. 

 if your Apple Watch says “you need more available storage to install a watchOS update.”  If your Apple Watch storage is full – Apple Support (UK)