Use the thin end of the slot stick (the end without the masking tape) to press a line in the cut edge. This mark is where the "point" of the lip will be.

Use the fettling knife (tool #4) to cut the clay under the mark just made. Cut at an angle as shown in figures 3 (circled) and 4 (cutaway of the voicing from the side). Do not cut your ocarina apart this way! This was done for illustration purposes only.
The purple area shows the the angle of the knife in relation to the voicing's side wall. Figure 5 shows the cuts when viewed straight on (white arrows).

The cuts, viewed from underneath.

Place the thin end of the slot stick (without the tape) on the mark previously made with it. Hold at a slight angle and press firmly in the direction of the arrows. (Figures 6, 7) The slot stick will slice away most (but not all) of the clay that is under the mark (indicated in purple in figure 7).

To prevent the clay above the mark from being distorted, firmly hold the frosting knife (tool #10) against it. (Figure 6)