Mic and speaker on Battery door bell plus are always off

I have just installed a battery doorbell plus for my sister and have found that when someone presses the doorbell the mic and speaker is always off and each time the mic button and speaker button in the app has to be turned on. This is useless for my sister as by the time she has managed to get the mic and speaker on because of elderly fingers, the person who rung the doorbell has left. How do I default the mic and speaker to be on?