Double-thread a leatherworking needle with thread that matches the color of your leather upholstery. Pull the end of the thread so it matches the opposite side of the thread evenly. This will make your stitches durable, preventing future tears along the seams.
Make a ½-inch fold of the leather upholstery on both sides of the broken seam. Pin the folds down with sewing pins.
Sew the folds together with the needle and thread, making stitches 1 inch apart, until you reach the end of the seam.
Tie the last stitch of the seam and trim it with scissors.