the instructions for the strap (neck tie) is on the sewing instructions page 8, it's bias cut strips that you sew together, then fold in half sew 1/4" seam and turn to make tubing. I don't understand why you would add a zipper. The dress was made tried out in every size and no one had trouble put the dress on. Also if you read the instruction carefully, these are not straps it's a tubing that goes through the casing of back and front. This is on page 8 of the instructions. I hope this helped.