What yoga exercises can relieve back pain?

Forward folds. Forward folds and hamstring stretches are good for the back. When you stretch our legs you are also stretching your back at the same time.
21 reasons 2 do yoga. #20: Curbs neck pain. Researchers speculate that enhanced muscle tone and less tension are why one study found that participants had a significant drop in the intensity of their neck pain after 10 weeks of yoga. Ref: AARP, 5/2017.
Yoga Back Poses: . Bharadvaja's Twist (Bharadvajasana I), Big Toe Pose (Padangusthasana), Bridge Pose (Setu Bandha Sarvangasana), Cat Pose (Marjaryasana), Chair Pose (Utkatasana), Cobra Pose (Bhujangasana), Cow Pose (Bitilasana) & Crane (Crow) Pose (Bakasana). REF:http://www.yogajournal.com/poses/anatomy/back.