This technique is simple. You need to go forward and to reverse successively while playing with the clutch (be careful : do it gently if you don't want to damage it).
Give the wheels a quarter turn 2 or 3 times forward and backward while turning the steering wheel quickly on the right and the left. The goal is to bring back sand under the wheels. After a short time, you will feel the car "rising" so give a straightforward accelerator stroke to take the car out. Easy...
If it doesn't work, deflate the tires (you can deflate until 8 psi). After getting unstuck, don't forget to reinflate up to 11 psi.