Can only record from one input on my UMC202HD

HI, there
I’m probably missing something really obvious, but I seem to only be able to use the 1st input on my UMC202HD. I recorded a couple of tracks using the first patch, but then tried to use the second port and nothing - no readings at all. Because I’m using Mics I’m recording in Mono but the software won’t recognize the existence of the second input - how do I fix this?