1. First click the Xiaomi Sports icon on the mobile phone screen, as shown in the figure below.
2. Then, in the opened page, click the shortcut link of mi band 4, as shown in the figure below.
3. Then in the open page, click the setting item of heart rate detection, as shown in the figure below.
4. Next, open the heart rate detection page and click the setting item of detection mode.
5. Finally, in the opened menu, click the menu item of auxiliary sleep detection.