The speaker has most likely been blown out from being played too loudly. Luckily the speaker is easy to replace. Follow the guide on the [[Lenovo IdeaTab S2109A-F Troubleshooting#Section_Tablet_sound_not_working_in_one_speaker|Lenovo IdeaTab S2109A-F troubleshooting page]] for the exact instructions.
Next time, try to mind how loud the volume is because sudden spikes of noise can cause damage. Using headphones while listening to high volume media will eliminate the risk of damage to the device.