Answer:
"Items you will need :
Set of small screwdrivers (computer repair set)
Soldering iron
Wooden toothpick
Solder
Everyone has experienced the moment when your headphones stop working. You jiggle the jack and they work fine until the day when jiggling the jack doesn’t work anymore and you can no longer hear anything. The problem isn’t your headphones, or that the player has stopped, but simply the solder on the jack has broken inside the case. You can learn to repair a headphone jack with a few simple tools.
Open the case by removing the screws that hold the case cover to the backing. Depending on whether you are repairing a headphone jack in a desktop, laptop or MP3 player, the screws will be located in different areas. Locate and remove all the screws. If the case does not pull free, stop and look for screws you missed.
Clean the old solder from the connection between the jack and circuit board. Do this by lightly touching the heated solder iron to the existing solder and then rolling the tip of a wooden toothpick in the soft solder to remove it.
Apply new solder to the connection. Hold the solder iron to the component pin (the pin exiting the back of the headphone jack) and touch the tip of your solder wire to the iron until the solder melts and forms a connection. Let the new connection cool for five minutes.
Test the player. Plug in your headphones to the jack and hit play. If you do not hear anything, turn up the volume. If you still do not hear anything, go back to Step 2 and begin again; your solder did not properly form a connection."
-https://itstillworks.com/12169700/how-to-fix-a-headphone-jack
