The maximum number of channels that can be recorded at one time is determined by the device driver. If, for example, the device driver supports 4 channel recording, then Audacity can record up to 4 channels at the same time. If you set Audacity to record 3 channels from that device, then Audacity will create 3 mono tracks. The device’s first channel will be recorded to the first track, the second device channel to the second track, and the third channel to the third track.
Set Audacity to record 2 (or more) channels. The second recorded channel corresponds to the device’s second channel.
Note that when recording exactly 2 channels, Audacity will create a stereo track (first device channel at the top, second device channel below). If you prefer to have separate (mono) tracks for each channel, you can split the stereo track into mono channels after you have recorded. See: https://manual.audacityteam.org/man/splitting_and_joining_stereo_tracks.html
Any unwanted tracks can be deleted by clicking the [X] in the top left corner of the track.
Record channels 1 & 2 (as a stereo track), then split the stereo track to 2 mono tracks, and delete the unused upper track.