Lower Microphone not working and my experience with Purism Support

When I make calls, I feel that I have to speak unnaturally loud for the other party to hear me.

For those of us less technically adept, can you recommend a series of steps by which the user can exclude a malfunction of the bottom microphone? That is, by using a combination of terminal commands, PulseAudio, and/or other steps can we confirm that this mic is actually functioning as intended?