this step is kind of fiddly, try to get a zip that is at least long enough to go around 3 sides of the controller. use a piece of ribbon or similar to bridge the gap along the bottom (to form hinge).
(for some reason my browser isnt letting me create notes on the images so i hope this makes sense)
glue around the inside edge of the controller and attach zip, use an old bank card to press the zip to the edge. work out which way round you want you wallet to be and make sure the middle of the zip is at hat side (see second photo for correct way round!). glue around the inner edge on the back plate and line up the zip, sticking as much as you can before unzipping (helps lining it up) finish positioning zip.
glue a strip of ribbon around the remaining edge then to the other plate. agin use the card to press the edges in.