How to turn the play back speaker on for the nikon d3100?

When i record a video on my nikon d3100, i would play it back and there would be no sound. Only an audio and microphone icon popping up. How do i turn on the play back speaker?

There seems to be no way to do so due to the device problem…

I would recommend you to report that problem to the device/mechanical service… Maybe, they can assist you with any kind of technical problem you are having.