Try on T-shirt. Mark for position of the zipper on the side of the arm.
Cut off the cuff of the shirt. Mark a 10” vertical line on the side of the arm of the shirt. Cut along this line.
Set the stitch length on the machine to 3-4mm for gathering. Stitch on each side of the slit. Pull thread ends to gather the 10” section to 6”. Tie off threads to secure.
Unzip the zipper. Place the zipper, front side up, on the slit with the bottom end of the zipper just above the slit. Open the zipper and sides of the zipper to the edge of the slit, over the gathering stitches. Fold under the ends of the tape at the bottom of the sleeve.
Set machine to a regular stitch length. Carefully sew the zipper in place checking frequently to make sure that the sleeve isn’t caught in the stitches.