Is there any way to tell my iPhone to use a different mic than my AirPods? I use my AirPods for streaming on YouTube. I don’t own a computer only an iPad and iphone. A friend bought me a usb mic not thinking that I don’t own a computer. So I bought a usb to lightning adapter. The mic has power but the sound comes from my AirPods not the mic. 

I only have wired and wireless AirPods and both have built in mics.

I want sound in from the wired mic and sound out to the AirPods over Bluetooth. 

Can I split the audio and use the better mic for recording?
Only in Live Listen mode (an Accessibility feature under Settings : Control Center).

But in general, no.  iOS devices switch both audio routes (in and out) to the last connected audio output device.  AirPods in your case.