change Volume of Audiomixergroups by script

In my game I want, that the Player can Change the volume of th sfx sounds and the Music separat. So I create two Audiomixergroups, to set the volume of them seperate. Now I created a Control in the GUI. Here are two slider, which are for Setting the volume of These two audiomixergroups. My Problem is that I don't know, how to set These Volums by Code. Here in the Forum I found, that I have to rigth click Attenuation of the audiomixergroup and to select expose Volume (of ...). I did it. But I still can't find out, how to Access this volume in the script.

Pleas help. Thank you!

(sry for my bad english...)