Customize PC Gaming Button Box Design

I don't know if I'm in the right place,(if that's the case can someone please point me in the right direction). My nephew has purchased what's known as a button box for his pc racing sim rig,the vendor had promised the software to control it but has failed to do so and is now not responding,leaving him with basically a box of switches. We need what I assume is known as a 'sketch' for it,I believe he has the relevant correct Arduino software installed. The box consists of 12 momentary buttons,4 on/off switches,1 two way momentary rocker switch and 4 rotary encoders/potentiometers and is connected to a Pro micro, marked AT mega 32U4. I have 40+ years as an Automotive diagnostics/electrics tech so can reliably provide any information needed as to it's circuitry,which appears to be a simple matrix layout.If anyone would be interested please reply with a price and timescale(children have no patience) Thanks in advance for your time.