When you set up a new song, use the template that exists for your device in studio one. Within that template, inputs 1 and 2 are configured 2 ways. They are configured as a stereo pair, and show up as input l and r, and then set up as mono inputs 1 and 2.
You want to record as a mono track so you can pan the channel in the stereo field. When you add a new track to the song, select mono for the track type, then select input 1 (not l or r) as the input for that track.