Find a note which works as a harmonic. Play it firstly as a harmonic. Then secondly play as a stopped note which you quickly release to the harmonic.
The use of harmonics is effective at releasing tightness in the whole hand because when the finger releases the thumb automatically releases as well.
Normally in fast passage work, once the finger has articulated the note it is best to release to less pressure while still maintaining contact with the string. There are times, however, when we need to maintain firmer finger pressure on the string. Some instances af this are:
when playing with a strong (especially a narrow) vibrato
the lower finger in artficial harmonics.
Finger Action - Introduction
Introduction to Shifting