Fold the excess fabric to create a waistband. If your fabric an be ironed, iron flat. Pin in place. You may need to trim some fabric at this time.
Pin the optional tie stash to the waistband.
If your dress did not have enough excess fabric to fold down either use the fabric you cut off or get some satin fabric of an appropriate color from the fabric store and fashion a waistband by cutting a long wide rectangle. If the fabric is thin you may want to add some backing.
Sew the waistband with a machine, making sure all the raw edges are turned under. This can be done by hand for a cleaner look.
Hand sew some hook and eyes to close the waistband and opening where the zipper was.
Trim any strings strings from the skirt.