Tibial internal rotation is a very common range of motion that most people are lacking. It is very important for overall knee health. It is also very important to have adequate amounts of tibial internal rotation for movements like the squat.
Tibial internal rotation is a coupled movement that occurs when the knee flexes and the ankle dorsiflexes. So if you have knee pain, a lack of ankle dorsiflexion, or trouble squatting, then make sure this range of motion is normal!
In a seated position on the ground, flex your hip and knee, and place your foot on the ground (see video below for visual). Take your arm on that side and place it between your knee and back of your thigh, hugging your leg towards your chest. Take your opposite hand and place it on the outside of your foot.
From here, pull your foot (and leg) into tibial internal rotation. You should feel rotational movement happening at the knee. Hold this stretch passively for about 2 minutes.
After 2 minutes of passive stretching, push your foot outwards into your hand isometrically (tibial external rotation). There should be no movement happening, but push hard into your hand for 20 seconds. After the 20 seconds, try to isometrically pull your foot away from your hand into more tibial internal rotation as hard as you can for 20 seconds.
Repeat this cycle 1-2 more times. Repeat on the opposite knee if needed.