The first thing you can do is that if you are currently using any application, you can just scroll down and see at the center of the screen if it’s showing an orange dot with the app name written. Then it indicates that this app is using your microphone currently. And another way to find out is that you can go to the settings of your iPhone, there you can tap on privacy and after that tap on the microphone and then you can have a look at the names of apps that you have permitted the microphone. If you find any app you don’t wish to give permission to, you can simply disable the bar.