Make a New Seam on Larger Garment
Using a sewing machine, carefully put the two knitted garments under the presser foot. I have set my presser foot to the mid position (out of left, mid, right choices). The left edge of the presser foot will travel alongside the edge of the template.
Using a closely matching thread and a mid-size stitch, sew your seam. Sew one more row of straight stitching very close to the outside edge of the first seam. THEN, zigzag a seam very close to the outside edge of the second straight seam.
IF you are uncomfortable leaving your template on the garment as you sew or if it would cause undue stress to the knitted fabric, use a contrasting yarn to baste a temporary seam.
Remove your template and sew your seam as given above, but on top of your basted outline.
If you do not have a sewing machine, use the yarn you knit the garment from and backstitch a new seam slightly away from the edge of your template.
Here is the sewn seam - you have to look carefully because I really matched that thread!