Step 1: Locate a Chipmunk. This is the most crucial step. You can't pronounce it if you can't find it.
Step 2: Observe the Chipmunk's Chip-ness. Note the way it chippily chomps on its food.
Step 3: Mimic the Chipmunk's Chip-chip-chip sound. Practice in front of a mirror until you achieve perfect pitch.
Step 4: Introduce yourself to the Chipmunk. Use the pronunciation you've acquired and say "Hello, Chipmunk!" with confidence.
This concludes the Squirrelly Guide to Pronouncing Chipmunk. Remember, practice makes perfect, so find a chipmunk and practice, practice, practice!