GarageBand Update - No Input

I've been using GarageBand to record my baby's heartbeat using a fetal doppler. I have noticed that since the most recent update, the "automatic input" option is no longer available...the in-app help feature still says to "tap the input button, then tap Automatic switch" to set input volume, but that button cannot be found. All I see when I tap the input button is "Noise Gate." The "Mic" button under the Input column is permanently gray and I cannot click that either. Is there still a way to connect an external mic/headset to the phone for recording? Or will I now have to switch to a new app? Thanks!