Wear your Apple Watch to bed with enough battery charge
Open the Sleep app on your iPhone
Set up Sleep Schedule and Sleep Focus
Turn on Track Sleep with Apple Watch in the Sleep settings
Make sure Wrist Detection is enabled on your Apple Watch
Put the watch on snugly before sleeping
Charge the watch before bed if battery is low
Sleep with the watch on overnight
Check sleep data in the Sleep app on iPhone
View sleep data in the Health app on iPhone
Update watchOS and iOS if sleep tracking is not working