There are several ways to add a sleeve to your quilt back. Here are a couple:
https://jacquelynnesteves.com/how-to-make-a-hanging-sleeve-for-a-quilt/
To make a quilt sleeve, cut a strip of fabric 8 1/2 inches wide by the width of your quilt, fold under the short ends twice and stitch a hem, then fold the strip in half lengthwise with wrong sides together and sew the long raw edges to create a tube. Center this tube on the back of the quilt about 1/2 to 3/4 of an inch from the top binding and hand-stitch it along the top edge, leaving a small pleat at the bottom to allow for a hanging rod. Finally, hand-stitch the bottom edge and both short sides of the sleeve to the quilt.
Check out this great video