Locate the center back seam of the skirt. Pick apart the hem stitching with a seam ripper at this point. If the skirt is lined, you may need to pick apart the waistband stitching to get at the hem stitching.
Pick apart the bottom 3 inches of the center back seam if your skirt does not already have a split or French vent there.
Iron the center back seam allowances of the outer skirt fabric and any lining fabric to the right.
Measure the length of the center back seam split and add 1 inch. Cut 1 piece of fabric that is this long and 7 inches wide.
Cut another piece of fabric that is as long as the Step 4 length measurement and 4 inches wide.
Pin the larger piece of fabric to the left side of the center back seam of the skirt, matching the fabric with the hem edge. Sew the fabric to the skirt, using a 1/2-inch seam allowance.
Pin the smaller piece of fabric to the right side of the center back seam of the skirt, matching the fabric with the hem edge. Sew the fabric to the skirt, using a 1/2-inch seam allowance. If your skirt has a lining layer, also attach the fabric to the lining.
Iron the seam allowances open. Fold the smaller piece of fabric inward, matching the folded edge with the original center back seam. Iron the fold.
Fold the larger piece of fabric inward, matching the folded edge with the raw edge of the smaller piece of fabric. The larger piece will cover the skirt split completely. Iron the fold.
Sandwich both extra pieces of skirt fabric together, with the outsides touching. Sew straight across the top edges from the center back seam to the outside edge. This will connect the pleat pieces.
Fold up the original hem and pin it in place. Fold the same hem length on the new pieces. Sew the hem across the bottom of the skirt.
If your skirt fabric strains under the weight of the kick pleat, add a small square of fusible interfacing to the top of the pleat on the inside.
Do not add pleat fabric that is heavier than your skirt fabric or the pleat will not hang properly.