How do I update my iwatch

See -> Update your Apple Watch

Update your Apple Watch – Apple Support (UK)

• Leave your Apple Watch on its charger while it's updating. Don't restart your iPhone or Apple Watch, and don't close the Apple Watch app. When the update has completed, your Apple Watch will restart on its own.

The answer will depend on which iPhone you have and which iOS it was updated to. This article may help. If not, let us know about your iPhone.

Update your Apple Watch - Apple Support