First of all I ironed it on the wrong side to remove the creases. I ironed it on a medium heat quite gently and the creases disappeared.
I cut a piece 15 inches long and 5 inches wide.
I ironed under about 1 cm (I am not sure why as I don't think it will fray much). I used a rajah cloth so I would not melt the fabric. Grab a zip. It doesn't matter what size as they will all be too big and will need to be shortened. Because pinning wil leave holes in the fabric. I used some hair clips to keep it in place.
Sew on the zip to each end.
Turn inside out and pin the sides. I pinned very close to the edge so any pin marks would end up in the seam and not be seen. Open the zip so you can turn it back the right way at the end. Sew the seams. I sewed over the zip a couple of times.
I used pinking shears to finish the seams and cut off the end of the zip.