If you are using two mics to two inputs on your interface, then you can't: A track can only have one input source selected.
So, you'd have to use two tracks, one for each input/microphone.
I'm not sure why you would be determined to record to just one track, but if you really need to, then the only way would be to mix the mics externally in a mixer of any sort and plug a mono output from the external mixer into one input on your interface. Select this input for the track in Studio One.
Honestly, though, you may as well just record to two tracks.
Hope this helps.