Usually when you have a technique like this you have 5 stitches, one being the center stitch. What you’re doing is passing the side stitches over the center st one at a time. Whether or not you have more or fewer stitches going over the center st, it’s still the same concept.
/ / C \ \
4 2 1 3
So you’re passing st one over the center stitch, then stitch 2 , 3, and 4. In order to do this, you have to move the center stitch from needle to needle. Just do exactly as the directions say, and you’ll see how it works.
You’re putting two stitches into the one on the row below, so you’re getting two extra stitches. You’re not using a stitch that’s already on the left needle.