Setu Bandha Sarvangasana (Bridge Pose) was named "God's gift to humanity" by B.K.S. Iyengar due to the phenomenal attributes of the pose and is included in the many of therapeutic sequences in Iyengar yoga particularly for deep-rooted organic problems.
We might not yet be up to the "full pose" or even if we are, we may want to start with Chattush Padasana (four limbs pose), a version of the pose named by Geeta Iyengar.
Geetaji shows a version holding the ankles. If you cannot grab your ankles, then use a belt as shown or you can also grab the sides of a yoga mat.
To protect your knees, make sure that your knees stay above your ankle so you don't overstretch the joint.