I had LEDs in a plane once.
I think you need a switch that HobbyKing sells. It’s really small so you should be able to hide it in your rig. Basically you plug it in to the Rx channel you choose, then assign a button on your Tx and it recognizes the pulse(?) for on or off from the signal terminal.
Around 7$ if I remember correctly. Wish I could recall its exact name for you