Which Apple Watch do you have, which iOS is installed on your iPhone?
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First, make sure that your Apple Watch works with the latest software. watchOS 10 is compatible with these Apple Watch models:
- Apple Watch Series 4 and later
- Apple Watch SE (1st generation) and later
- Apple Watch Ultra and later
Not all watchOS 10 features are available on all devices.
Updating to watchOS 10 requires iPhone XS or later with iOS 17.
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- Make sure that your iPhone is updated to the latest version of iOS.
- Make sure that your Apple Watch is at least 50 percent charged.
- Make sure that your iPhone is connected to Wi-Fi.
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copied from: Update your Apple Watch - Apple Support
Did you try the troubleshooting mentioned in this article?
If your Apple Watch won't charge or it won't turn on - Apple Support
If your Apple Watch still can not be updated, contact Apple Support