Pin short sides of skirt (yes, the short sides are the sides we serged/zig-zag stitched before we attached the skirt to bodice) with right sides together.
Stitch stopping 12.5cm(5") from top edge of skirt. Press seam open. Continue pressing open the seam allowance of the unstitched 12.5cm(5"). Stitch around the vee-shaped gap close to the zigzag/serged edge, pivotting at bottom of vee..