lay the two edges to be sewn one above the other. Bring your tapestry needle out through the middle of the first stitch on the right-hand side of the bottom panel, and take it under the corresponding stitch on the panel above.
reinsert the needle through the middle of the same stitch on the bottom panel, bringing it back out through the middle of the next stitch along. This should give you a v-shape. Repeat this along the join, pulling the yarn until the sewn stitches are the same size as the knitted ones