Click on the audio clip that contains the audio you wish to drop in pitch. Audio clips are the rectangular blocks in the center of the window that contain jagged waveforms, visual representations of the sound.
Click on the "AudioSuite" drop-down menu at the top of the screen, and select "Pitch Shift" from the "Pitch Shift" menu.
Adjust the slider next to the word "Coarse" to change the pitch. Dragging the slider to the left will lower or "drop" the pitch.
Select the "Preview" button at the bottom of the Pitch Shift window to preview the effect. Adjust the "Coarse" slider until you are satisfied.
Hit the "Process" button in the lower right portion of the Pitch Shift box to process and finalize the effect.