Apple Watch upadate. Unable to Check for Update

Try and update via your Apple Watch itself instead

If your Apple Watch has watchOS 6 or later, you can install updates without your iPhone:

1. Make sure that your watch is connected to Wi-Fi.
2. On your watch, open the Settings app.
3. Tap General > Software Update.
4. Tap Install if a software update is available, then follow the onscreen instructions.