How to set Redmi Watch 4 to light up the screen when I raise my wrist?

Setting method: Go to [Settings] >> [Display & Brightness] >> [Wrist Lift Screen] >> Timer On/All Day On/Off. Timer On will have the option of effective period, so you can set the effective time according to your needs.
Slide up the main page of the watch dial, open the control panel, tap the icon of Wrist Lift and you can quickly switch on/off the Wrist Lift status.
Note:
When the watch is in sleep mode, it will automatically turn off the wrist lift screen. Setting method: Go to the [Mi Fitness] App >> [Device] >> [Sleep Mode] >> Set rest time.