The iHealth Edge automatically enters in sleep mode. So you have nothing else to do than to wear on your wrist when you go to bed.
It also exits the sleep mode automatically when you wake up and make a few steps.
A sleep summary is displayed on the screen and indicates the total sleep duration and sleep efficiency. This summary is available for 30 minutes after the other information visible on the screen.
*credit to Sylvain of iHealth Labs EU
https://helpcenter.ihealthlabs.eu/hc/en-gb/articles/211768225-iHealth-Edge-AM3S-How-to-enable-disable-sleep-mode