Apple Watch series 7 system update problem

Hello ThaiSong,

Thank you for reaching out in Apple Support Communities. We understand you're unable to complete the update for your Apple Watch. We can help point you in the right direction.

To help troubleshoot this behavior, we recommend to follow these steps:

"If you need help updating

Try these steps:

1. Make sure that your Apple Watch connects to its charger. 
2. Restart your Apple Watch. Press and hold the side button until you see Power Off, then drag the slider. To turn your watch on again, press and hold the side button.
3. Restart your paired iPhone.
4. Try to start the update again. 

If the update won't start, open the Watch app on your iPhone, tap General > Usage > Software Update, then delete the update file. After you delete the file, try to download and install watchOS again.

Learn what to do if you see 'Cannot Install Update' when updating Apple Watch."

Update your Apple Watch - Apple Support

Following these steps can help complete the update. Please keep us posted with the results.

Kind regards.

Good afternoon ThaiSong,

Thanks for letting us know you were able to complete the watchOS update. Enjoy the rest of your day!