You can output the sound through the microphone by selecting the speaker unit.
Bluetooth Loudspeaker - Apps on Google Play
Mic to Speaker - Virtual Mic on the App Store
Microphone live bluetooth - Apps on Google Play
How to Boost Microphone Volume on Android: 15 Steps
Live Bluetooth Microphone App - Apps on Google Play
Microphone - Apps on Google Play
Microphone - Apps on Google Play
Wireless Microphone - Apps on Google Play
Live Bluetooth Microphone: Mic – Apps on Google Play
Bluetooth Loudspeaker - Apps on Google Play
Live Bluetooth Microphone: Mic - Apps on Google Play
Microphone Pro (No delay) - Apps on Google Play
Tzumi Rock Solo Karaoke Mic Speaker Bluetooth Built-in Smartphone Holder Black