You want to keep working in the same way you have been. If we call their "next row", "next row", etc. rows 1, 2, 3, 4.
Row 5 will be:
K6one less than the beginning of row 3 sts, SSK, k1, k2tog, k6(6,7,7,8,9,9). [You will now have 15 (15,17,17,19,21,21) sts depending on the size you are making]
Row 6: K7 (7,8,8,9,10,10)[1 more than at the beginning of row 5, this will be up to the middle st], p1 [the middle st], knit 7 (7,8,8,9,10,10)to the end.
By this time you should be able to see what is happening. On the right side you want a line of knit stitches going right down the center of the flap and you will decrease right before (SSK) and right after (k2tog) that line of knit stitches on every right side row. You will lose 2 stitches with each decrease row.
On the wrong side rows you will always knit to the center stitch, purl the center stitch, and then knit to the end.
Keep working that way until you have only 5 stitches.