Using channel 2 as mono audio

Hello,

I have two XLR audio inputs into my camera: a lavalier (recorded to channel 1) and a shotgun mic (recorded channel 2). I wasn't impressed with the lavalier audio for my film, and want to use the shotgun mic audio exclusively in mono. I know how to isolate channel 1 and make the video mono with only that channel, but how do I do this in Openshot if I want to isolate and use only channel 2? This seems less straightforward, as when I select "mono (1 channel)" under audio settings in the export video dialog box, it keeps trying to use channel 1 even though I deleted channel 1, which results in blank audio.