Today, I'm repairing my earphone which L side is working and right side sound to be fixed. This is a pretty simple process and is a good beginner DIY project.
For this I'm removing earphone jack and replacing with 3.5mm Male Steel Jack I have no knowledge of making such things, I surfed a lot on internet so I tried myself and using tools like soldering iron first time, overall it's came out awesome and I'm very happy, I hope you like this project.

Materials Required for Repairing Earphone :-

3.5mm Steel Jack
Soldering Iron
Soldering Wire
Wire Cutter
Plier

Note: - Plier and wire cutter tools aren’t necessary, but they just help make the process go quicker.

Step 1: Inspect Before Clinical Procedure

Inspect one last time before clinical procedure, maybe rubbing or twisting can revive your earphone.

Step 2: 3.55mm Male Steel Jack (Role)

Mostly Earphone support 3.55mm connection, Check it before purchasing, So that you're not messing in between 2.5mm or 3.5mm connection.

Step 3: Make a Cut in Earphone Plug

Now, Cut the earphone jack just above 4 or 5 inches, with the help of plier and remove with cutter. After removing jack cut the extra supporting fiber wire.

In this earphone got 4 wires.

Red (Right Side Noise)
Green (Left Side Noise)
Golden (Ground Connection or earth)
White (Supporting fiber wire)

Step 4: Preparing Clinical Procedure

Here I'm removing wire coating with match stick, make sure you do not over burn the wires, after removing
coating simply pushed all three wire in Steel Jack Casing.

Step 5: Begin Clinical Procedure (Soldering)

Here, I'm slowly making soldering in all three holes. After Soldering make sure they are not short to each other.

Step 6: Final Look on : Repaired Earphone

After soldering, Close the casing of jack and check your earphone on your mobile.
This is the repaired earphone, now i can re-use my earphone again. I hope you like this project. Thanks!