Sitting on a bench or table is best for this.
Place the tennis ball under your hamstring starting at the top by your sit-bones. Then easing into the balls...breathe!
Wiggle side to side to see where there is any restrictions. You can also lift the leg up until you feel a slight pull and then release back down.
Repeat this 3-5 times. Then move the ball a little bit down towards the knee.
Repeat as above then continue to move the ball down even further and repeat.
You can also move the ball inwards more towards the inner thighs or to the outside.
You are in charge of the pressure. If it's too much then take the weight off a little. You should feel the discomfort reduce. If it increases then move off and look again.
Little and often is best but especially before activity and after periods of inactivity.