TKG Chrome App works the best. You have to make your layout on
KLE if you didn't already. Once you set up your layers, you can set up your function keys. The dropdown menu will let you set-up your backlight toggle.
I'm not the greatest at explaining, if you need any more help, feel free to shoot me a PM.
Here's a quick example layout:
Function keys were set to the left cluster. You can then set them to whatever you want.