If it doesn't have a phase inverter switch and you don't have a way to record the two mics on separate tracks, you'll need an inline phase inverter. MsHilarious used to sell one on the Naiant studio store, but I don't see it currently.
The only one I could find online was $65, which is insane considering that all you have to do is rewire an XLR cable with the + and - wires swapped on one end.... Of course, the $65 one also had a DPDT switch....
I had to get a few of those for a session. They aren't terribly expensive and they just look like a silver cylinder. I think they were about $10 or $20 each.