It is typically a buildup of earwax, that went into the speaker/headphone itself, blocking the speaker.
1. Use a toothpick, and on all ports, clean as much earwax as possible. Just scrape it off, do not put the toothpick in the speaker itself or puncture it.
2. Turn your earphones, on, go into your settings for your device and turn the mono audio slider, all the way to the non working speaker. And play audio, and blast the speaker, gradually turning the volume (essentially you want to be playing audio in the speak, getting max volume). Do this until you can barely hear the volume. Once you can, go back into settings, and even the mono audio slider again (you don't have to do that, it just helps).
3. Now, let the headphones sit, for a day roughly, If it still doesn't work, then let it sit longer. If it still doesn't, the speakers are clogged.
4. My tip to you, is clean your ears guys.