Align the two edges that need to be sewn together, with the right side of the fabric facing out.

Thread your sewing needle with a length of yarn and fasten it to the wrong side of the fabric.

Insert your sewing needle under the horizontal bar between the first and second stitch on the right edge and pull the yarn through.

Insert the needle under the corresponding bar on the left edge and pull the yarn through.

Insert the needle under the next bar on the right edge and pull the yarn through.

Insert the needle under the next bar on the left edge and pull the yarn through.

Repeat steps 3-6 to create your invisible seam.