Default [Q] Default GamePad action mappings

I have a JXD S7800 and, when keypresses are not captured by applications, there are a couple of bizzare defaults.

The "START" button is mapped to home (even though the device already has a dedicated home button), and the "C" button is mapped to Enter/Accept

Ideally I'd like to remove the "Start --> Home" mapping completely, and remap "A" to "Enter/Accept" instead of "C".

I'm guessing there's a file I can edit somewhere that will do this. But what file and where?