Mono out on DDJ-SR2

Hi Guys, please excuse my ignorance as I'm an IT Guy helping a client out here.

This is a restaurant sound system controlled by a Nuvo controller.

They have a DJ coming in with a DDJ-SR2 system we have XLR inputs all over the restaurant. The AV guy that setup the system told me this is a mono setup and that any mixer that connects should connect in mono. How do you switch this DDJ-SR2 to momo? The DJ bringing in isn't sure? I put a question mark because I figured he should know since it's his device. Maybe he is new to it. Anyway I appreciate any and all help here. 

Thanks

Josh