Allow the jaw to release into gravity. Place your finger tips on the jaw to ensure that it remains calm and open during this tongue exercise.
Gently reach the body of the tongue toward an /i/ (EE) shape, then release the tongue back toward neutral. Explore this movement several times, aiming for slow, smooth, and easy movement. Remember to continue allowing breath to arrive and depart.
Gradually begin to increase the speed of this movement, continuing to breathe over the changing shape of the space inside the mouth. Ensure that the jaw and throat remain calm and passive as the tongue moves. Only move at a speed at which you can be successful. Rapid movement comes with time and practice, not with greater effort.
After a few breath cycles, see if you can sneak some vocal vibration into the exercise without adding additional effort in the tongue, jaw, or throat. Remember to allow the breath to initiate the vibration.
When you’re finished, try to take your work with you into the next thing you do.