Hi there Lee NZ,
If you are unable to update your Apple Watch, let's first ensure your iPhone is fully updated since this can install bug fixes and security content that can resolve issues like this. These steps from Update your iPhone or iPad show how:
1. Back up your device using iCloud or your computer.
2. Plug your device into power and connect to the internet with Wi-Fi.
3. Go to Settings > General, then tap Software Update.
4. Choose the software update that you want to install. You can choose to stay on iOS or iPadOS 15 and still get important security updates. Or you can choose the option to upgrade to iOS or iPadOS 16.
5. Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.
If this continues after updating your iPhone, follow the recommendations here next to see if they help: If you see 'Unable to Verify Update' when updating Apple Watch
If you are still unable to update your Apple Watch, reach out to Apple Support. They would be the best equipped to investigate this issue further. Contact them here: Apple Support
Cheers!