Android app not allowing external microphone to be selected

Having a bit of a panic! Getting married on Sunday and we're streaming it via Zoom. However, as the camera (Android phone) will not be near the 'action', I bought an external wireless mic to capture the audio, actually I got 3 to test the audio quality and was going to return 2. They all work fine when recording audio via a sound recorder app but when I tested with Zoom, it defaults to the device's internal mic and does not offer a drop down to select the external mic. Can anyone advise if it is possible to select an external mic in the Zoom app on an android phone, and if so how?

Thanks in advance.