Diagnosis
The clean cycle is a timed function that requires water and soap. It's not working because the jar is likely not full enough or the program is interrupted.
How to Fix It
Fill the jar with warm water to just above the blades. Add a drop of dish soap. Secure the lid. Press and hold the 'Clean' button for 3 seconds. It should run a 30-60 second agitating cycle. If it stops early, you may have lifted the jar.
If That Didn't Work
The touchpad control for that specific button might be faulty. Try pressing firmly in the center of the button. If other buttons work, the membrane switch for 'Clean' is dead.
Heads Up
This is not a self-cleaning function for dried-on debris. You still need to scrub the jar after the cycle for stuck-on food.