AUX OFFSET on Contintental 139 mp3 radio

[t0neloc]

Hi.
I've successfully added an aux input to the radio on my 2014 panda pop.
The manual states that there is an option AUX OFFSET that allows you to set the volume relative to the radio etc. but this option does not appear in the menus.
I reset the radio with the AUX input active and it's still not present.

Any ideas?

Thanks