KoboToolbox's audio questions are designed to be used in sequence with other questions in your form.
If you want to record during the entirety of the interviews, load up your audio recorder (e.g. the built-in one or Recforge Pro) and start recording and leave it running in the background before filling in data in KoBoCollect.
Expert Tip: Add notes at the beginning and end of the form to remind the enumerators to start and stop recording respectively.
If you do choose to go the route of recording entire interviews in the background, be sure to remove any audio questions from your form as they would conflict with the ongoing background recording.