Place a single tennis ball just above your pelvis (and below your ribs). Then easing into the ball, lean against a wall.
You want to bend forwards whilst pushing the ball back into the wall. It sometimes helps to come onto the side slightly. You are looking for a little discomfort so if there are a few spots that feel uncomfortable (NOT painful) then stay there and breath.
You should feel the discomfort reduce. If it increases then move off and look again.
Stay on one side as you find a couple of different 'spots' to work on.
Repeat on opposite side.
If something doesn't feel right then move away. Mobilising restricted tissue can be uncomfortable but it should not be unbearable. Please use common sense!