CEC RPi3 map a button

Hi,

i’m freak out to map a botton of my remote in my TV LG 47LA667S
[Image: LG-Remote-Control-FOR64.jpg]

I wish to use the right blue botton ( Channel UP and DOWN ) but when i tried to map it with keymap editor addon, appear in the tv the message: Only available in TV Input. Do you want to select TV Input ?