How Can You Change Which Microphone Is Used During Calls?

My LG G4 phone's main microphone is broken but it's secondary microphone is working. That is, during ordinary calls or voice recordings, the microphone doesn't pick up any sound (completely dead) but during speakerphone calls or video recordings that microphone works fine. Is there any way to permanently redirect the primary microphone to the secondary one, so that for ALL calls, the secondary microphone is used to pick up sound?