I am having a similar issue to this stackexchange post: https://unix.stackexchange.com/questions/246661/how-do-i-get-mint-to-recognize-my-laptops-microphone-as-a-mono-input-instead-of
I tried to follow their solution and load a pulseaudio module to remap a single channel from my mic into a new mono source.
when I tried adding the command to the ‘default.pa’ file and rebooting, it caused the entire audio system to not connect until the line was removed. I then tried installing pactl and loading the command from the terminal but I got a ‘connection refused’ error.