The chromatic scale or twelve-tone scale is a musical scale with twelve pitches, each a semitone above or below its adjacent pitches.
To play a chromatic ending while holding the upper C note, you can play an ascending ending by striking the chromatic scale starting with the lower C and ascending to the middle C, while slowing the ascent on the last few notes to give it effect.
To play a descending ending, hold the upper C note while consecutively playing the middle C and descend to the lower C chromatically, slowing the descent on the last few notes for effect.
This video link demonstrates the technique, which can make anyone sound like a professional.
Tips and Techniques from Marco Mendez.
How to play a chromatic ending.