Microphone Not Recognized

I’m using Audacity 2.3.3 on my MacBook Air Catalina 10.15.2. Audacity doesn’t seem to know that I have my headphones/microphone combo plugged in. The Mac recognizes it but the drop down menu next to “Built-in Microphone” doesn’t give me any options to select “Microphone” or whatever it should say; there are no other options. Any help would be appreciated.