How to set up sleep tracking on the iPhone
If you haven’t set up the Sleep feature on your iPhone, you’ll need to do this first.
Head into the Health app, locate Sleep and tap Get Started. Then, follow the instructions on the screen to set up sleep tracking on your iPhone.
How to edit your sleep schedule on the Apple Watch
You can edit your sleep schedule on your iPhone or directly on your Apple Watch.
To edit it using your Apple Watch, open the Sleep app on your watch and tap the sleep alarm icon in the top left corner. Make any adjustments to your sleep schedule – including Wake Up and Bedtime times and alarms – and tap the left arrow in the top left corner to save the changes.