Step 1: Tools and materials
For tools you will need scissors (or a sharp knife), a lighter and a short length of nylon cord that can be pushed through the plastic tubing with ease. It should be longer than the length of tubing you will cut (see later step).
The lengths given here are what I used and worked well for my particular zipper and gives a loop through which a finger comfortably fits. You may want to experiment with different sizes.
Step 2: Cut cord and tubing
You don't need to heat-seal the end of the cord yet.
Make sure that the thin cord is longer (at least 5cm (2 inches)) than the tubing.