This is a step that isn't structurally necessary. More of my dragons than not have "under belly armor plates". If you don't want this detail no biggy. If you do, start with rolling out a long piece of clay on the next to the thickest setting on the pasta machine. Cut a long strip that tapers on both ends. Do a test drive of how it fits before you apply. Once your under armor section is cut to the right size gently press onto the underside of the dragon starting where the jaw meets the neck and going as far down the tail as you want. I normally go about half way. Use the butt end of a brush or a larger needle tool to roll down the edges of the armor piece. This will smooth the piece into the body but not blend it in. To add the details of the armor use a fine needle tool and mark lines at the interval of your choice from top to bottom.