Press the keyboard backlight hotkey, usually Fn + F4 or Fn + F7 on ASUS laptops
Look for a key with a keyboard light icon and use Fn + that key
Press the hotkey repeatedly to cycle through backlight levels
Check the ASUS Armoury Crate or MyASUS app for keyboard lighting settings
Enable keyboard backlight in BIOS if the option is available
Make sure your laptop model actually supports keyboard backlighting
Update ASUS hotkey or keyboard drivers if the light does not turn on
Restart the laptop and try the hotkey again