Bottom loud speaker not working

The bottom speaker of my HTC One M7 is not working. When i play music out loud the music comes out of the top ear piece speaker but the bottom one just ticks and ticks with no sound coming out. no matter what sound i play out loud this happens, including when the phone rings.

i woudl repair this myself but i cannot find a good guide anywhere on how to get it in and out risk free.

Does anyone know of anything that could have caused this or is a replacement the best way to go?