RETROARCH - NEED HELP WITH INPUT CONFIG

[PiperCalls]

I have a 2-player MAME cab now. Starting to look into adding other emus, I've tested Retroarch and really like it. I've done some research and can't seem to find a way to assign keyboard keys to the 2-player controls within Retroarch. I've tried it inside the RGUI but this doesn't work and I've tried editing the CFG file but nothing seems to work.  I have an ipac keyboard encoder wired to my CP so I would like to just assign keys to control 2-player (like what I'm doing in MAME) in Retroarch if it is possible. Just wondering if this is even possible and if so if anyone could lend some guidance?

Thanks...Piper