Before you start a session, all you need to do is click on the musical note or the soundwave button at the bottom. If you click on the current guide, it will then provide a list of potential voice options for that speaker. You can switch by tapping on the guide you'd like from the list that's generated!
Note: Only certain voices are available for certain sessions (Fr. Mike's voice is not available for all of our sessions) Additionally, only one voice may be available for any given session.