Igo Primo - background music not working via aux input (MP3 Player)

Hi,
I used to be able to play background music via an attached MP3 player with Igo Primo , and now since the car battery was disconnected it no longer works (Now defaults to SD card music I think) - this is on an Xtrons car stereo

I had this issue before and I know that there is a software switch (hidden menu somewhere???) to change the input from SD card to the aux input (to use an MP3 player) but for the life of me I cannot find the ONE Google result that told me how to do this (I would have thought it was quite a common thing to be honest?)

I would appreciate some help please as it's driving me nuts!

Thank you....

on old units, it used to be go to settings, press 1 3 5 7 9 on the remote.