Apple watch stuck in recovery mode

If even a force restart can not get your watch to start up normally, you will have to get the Apple Watch serviced.

Visit an Authorised Apple Service Provider or Apple Store next to your place, or contact the Apple Support directly:

Apple - Find Locations

Apple Watch Service and Repair - Apple Support

Phone numbers Apple Support

Did you already try these suggestions?

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Try these steps:

1. Make sure that your Apple Watch is connecting properly to its charger. 
2. Restart your Apple Watch.
3. Restart your paired iPhone.
4. Try again to update your Apple Watch.

If the update won't start:

1. Open the Apple Watch app on your iPhone.
2. Tap General > Storage.
3. Delete the update file.
4. Try again to update your Apple Watch.

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copied from: Update your Apple Watch - Apple Support

Erasing and pairing it again to your iPhone is the only way:

Unpair and erase your Apple Watch - Apple Support

You can also try the steps in this article, if you haven't already:

If your Apple Watch shows an iPhone and a watch or a red “!” - Apple Support

Make sure the Wi-Fi you're using is not protected by a VPN or other security. If so, try another Wi-Fi network and try again. That worked for me

I’d this happen before so I can help. If it’s stuck in recovery mode, force restart your Apple Watch. Press and hold the Digital Crown and the Side Button together until you see the Apple Logo boot-up screen. Hope it helped and have a good day!