Cut a section of the leg to fit into the front section that is left open when you overlap the two sides. Sew along the seam, following the seam.
Sew the two sides of the insert. Do the under seam first. Then sew the top seam starting at the zipper.Turn the skirt around to the back. Overlap one side of the inner thigh over the other one. Draw a two seam lines straight down the back connecting with the original seam near the top. Sew the two lines to match the original back seam.
Turn inside out. Cut the extra jean away. Either serge or zig zag stitch the edges.
Cut the skirt to the length you want. Sew the bottom hem.