The next step is to carefully cut through all layers of fabric down the middle of the two rows of stitching. Be careful not to cut into the welt. Start a cut in the middle of the rows and work your way almost to the end. Stop apx 1/4 or 3/8 " from the end of your stitching. Cut the other direction to the other end and stopping again at 1/4 or 3/8" from the end.
If you turn the fabric over and open up the flaps you will see where I stopped. At this point you need to carefully cut the diagonal lines up to the end of the the stitch marks. Be very careful how far you snip as you don't want to cut past the stitch lines.
After you have clipped both ends in this fashion, push the pocket through the opening you just made and flatten out the welt. The next part is very important, so don't skip this.
Pull the garment back some so it looks like this. Pull up the small triangular piece and sew "very" close across the welt as seen above.
After you have sewing that last little section on both ends, straighten and flatten the welt out and iron well.
Finished product. I used chalk, so these markings will come out. :)