I think the MiniNova isn't meant to be run in mono. But there's nothing stopping you from just connecting the left to the interface Line in and using that. Maybe the Nova has a built in pan on the output? Haven't used one myself. You could also get an adapter to connect the right TRS channel into the XLR plug. But the volumes would be wildly different and you'd need to fix that in your DAW. Not much of a hassle, but still noteworthy. Also might sound a bit different, due to the impedance differences between the line input on your interface and the mic input on the XLR.
Typically when synths have a specific Mono out, it's labeled right next to one of the outputs. Like seen on the picture below.
----Overall, I'd recommend getting a interface with two line in inputs. Both of the ways to connect the MiniNova to this interface are sub-optimal.