Right click on the speaker icon in the taskbar notification area. Select sound. Select playback tab, double click on speakers, select level tab in speaker properties click on balance. Now adjust the sliders so that one side cuts out while sound is still coming from the other side. Repeat for the other speaker.
You also try using VLC -> Audio -> Visualizations to see if VLC is processing the audio signal from both audio channels as it may not be your speaker itself that is of fault but a component in the audio processing circuitry instead.
As for replacing a speaker, googling or youtubing for “teardowns” or “repairs” plus your model number usually produces positive results.