This exercise involves sitting on your back and bending your knees at about a 90 degree angle. You should keep your head on the pillow for more stability and your hands on your knees. The next step is to try to rotate your knees in a clockwise direction for twenty seconds, then in a counterclockwise direction for another twenty seconds.
You should repeat this process at least three times or until you feel that it is enough. Moreover, if you want to increase the level of difficulty, you can also lift your head slightly to tense your abdomen. You should try this exercise every day.