Go to Jalan Pasar or any electronic store and get a soldering iron + solder wire + soldering paste..
After that buy from Jalan Pasar/electronic store a 3.5mm audio plug..preferably the metal gold one that I showed here
A plastic one works well also but I bought a RM1.50 metal/plastic ones and they are useless..the better one I bought is RM3.50 which looks almost like the gold one


This is what it should look like inside of that plug and you have to solder the wires to 3 parts of it..

Will have 4 wires but 2 are ground which should be twisted together..another 2 is left and right
If your cable has insulation like the one showed here you need to strip it..if it is an enamel coating you need to burn it off with a lighter
Melt some soldering paste on to the wire so that it will stick easier to the metal when soldering..
A lot of trial and error as sometimes the color of the wire is not exact and I have mixed up left become right and right become left in my first try..
Important note is that the 3 parts should not touch each other when you close everything up or else it will sound weird..
If you go to Audiophile section they will also ask you to go to Jalan Pasar and so on because I asked there last time..if you feel adventurous give it a try