Apple Watch sleep data

Source: Business Insider

"Apple doesn't currently offer their own sleep-tracking app for the Apple Watch. You can download an Apple Watch sleep app from the App Store that will use a combination of your movement and heart rate to monitor your sleep."

https://www.businessinsider.com/does-apple-watch-track-sleep-apps-review

But it might not be long ...

"The App Store listing for Apple’s Alarms app for Apple Watch references an unreleased Sleep app"

Source: The Verge

https://www.theverge.com/2019/10/7/20902950/apple-watch-sleep-tracking-app-beddit-watchos-iphone

Hello, currently there is no specific pre-installed sleep monitoring app. You need to use third-party apps that you can find on the app store dedicated to apple watch