I started by removing the thread from the side seams and the rear waistband. I removed the lining from the back waistband and cut at the side seams leaving an additional one inch of lining fabric from the back lining on both sides.
I used the leather back to draft a paper pattern to use for the new back lining and new back fabric. For the fabric piece, I added a foldover waistband and 1 1/4" hem allowance.
I had the black ribbed fabric in my stash. After cutting the new fabric back, I folded over and stitched both the waistband and the hem. I stitched the lining to the waistband and then stitched back and front lining pieces together. Next I cut and inserted the elastic into the back waistband.