CUT out pocket and upper flap out of your main fabric.
CUT out smaller strips of “lining” to cover ugly zipper on reverse.
MAKE 1/2″ double fold “bias tape” from 2″ wide strips of fabric. It has to be enough to cover the outside parameter of the pocket. It doesn’t have to be bias cut since we are only dealing with straight lines.
***** NOTE: When I first made this (and when I was taking pictures) I made the pocket WAY to huge. It should be the right size to be able to contain your sling, but not too big to interfere with adjusting the sling.