"Anchoring" is an effective way to train your body to quickly relax by making an association in your brain between a state of relaxation and touching a specific spot on your hand or wrist.
In this relaxation exercise, I'll describe using your right thumb as an anchor spot.
Once you are relaxed, you will use anchoring to associate the action of squeezing your right thumb with a state of relaxation. Once this association is made, you will be able to trigger relaxation quickly, simply by squeezing your right thumb.
Practise this exercise several times to firmly ingrain the association in your brain. After a few sessions, you will notice that you can relax immediately just by squeezing your right thumb - anytime, anywhere.