Turn off backlight for 3.5inch Rpi LCD (ILI9486)

[JayceCao]

I am using the ILI9486 LCD on my ESP32 project.
However, I am having problem to turn off the backlight of LCD using backlight register.
It seems not work even for dimming the backlight.
I heard that we can use GPIO to turn off the backlight.
I would like to ask if everyone have the pinout or anyway to turn off the backlight.
Best regard.