Stuck in preparing

Other users having a similar issue deleted the watchOS update file on the iPhone.

To do that, open the Watch App on your iPhone, go to General -> Storage -> look for the watchOS update file and delete it.

After that, force restart your Apple Watch by pressing and holding the Digital Crown and the Side button together for about 10sec, until the Apple logo comes back again.

In case you are using a VPN, disable it. Then try to update again.

Firstly, ensure that your Apple Watch is connected to its charger and that it's within range of your iPhone. Sometimes, a stable power source and a strong Bluetooth connection can help facilitate the update process.

If your Apple Watch continues to be stuck in the "preparing" phase despite being properly connected, you can try restarting both your Apple Watch and your iPhone. A simple restart may help resolve any temporary software glitches or issues that could be causing the update to stall.

Additionally, make sure that your iPhone is running the latest version of iOS. Sometimes, compatibility issues between your iPhone's software and your Apple Watch's software can interfere with the update process. Updating your iPhone to the latest iOS version may help address any compatibility issues and facilitate a smoother update for your Apple Watch.

If restarting your devices and ensuring they're up to date doesn't resolve the issue, you may need to consider other troubleshooting steps or contact Official Apple Support for further assistance. They can provide guidance on additional steps you can take to troubleshoot the issue or offer further support if needed.