This step may seem heartbreaking but you'll have to cut the headphone wire in three places. Around 1" before the three wires intersect is where you'll cut and strip the 3 wires.
Once you have the 3 separate strands of wires apart, you'll need to cut paracord that's the same length of the wire.
Next remove the inner strands of the paracord, leaving just the outershell
Finally, string the headphone wire through the outer shell of the paracord, this can be be done by "scrunching" up the paracord and then extending it over the wire. This may sound strange so refer to the video on the first step if you're confused!