Can't map 'back' action

Hi, I connect to my Lakka (2.3.1) pad (PS3 compatible) and have problem to navigate GUI via pad - can’t recognize in configuration to bind pad button back action (backspace in keyboard). Any help?

I went ahead and made a new topic for you.

So, the back/cancel action is mapped to retropad-B (you can swap it to retropad-A in the input options). Whatever button on your gamepad corresponds to retropad-B should do it. On a PS3 pad, it’s typically cross/‘X’