Volume control with M1 MacPro touchpad

Hi all,
I’ve just got a new M1 Mac Pro from work, just adding Roon to it and using a spare Dragonfly Back I have knocking about.

Does anyone now how I can use the Mac’s volume controls to control volume in Roon when it’s in exclusive mode as it’s just doing the desktop audio and not that in Roon?.

I can’t seem to choose the DFB from the volume bar when Roons playing . I am not that familiar with setting up MacOS so any advice would be welcome.