Don't blow, just hum. When we play kazoo big side in the mouth, don't blow like playing harmonica. You need to hum the tune, the vibrations of the vocal cords make the flute diaphragm vibrate and sound. You can change the tone of the kazoo by rotating the lid on the flute diaphragm. When the lid is twisted too tight, its sound will be more crisp. On the contrary, its sound will become hoarse.
Note: If one doesn't make a sound, just tight (push down or twist) the ring that has the membrane. Problem solved.