I'm going to give you guys some tips on doing a back walkover on the beam. I think it's really important that you have your own sense of comfort when you're on the beam, so just spending a lot of time on the beam is really important.
Once you can walk around, do turns, a half turn, full turn, cartwheels. Once when you can do a lot of basic skills you become more comfortable on the beam, because going backwards on a four inch surface can be a little frightening and it's definitely something that causes a lot of mental blocks with young girls when they start to gymnastics.
Most importantly I think is confidence and then the next part I would say is you need to just practice a lot. Practice a lot on the floor, the low beams and practice with a lot of spotting on the higher beam, once you become more and more advanced. So it's really important when you do this skill to stay tight.
Your whole body needs to stay tight. Your arms have to stay really close together so they don't fall fall apart, and you miss the beam. So keep your hands together on the beam, point your toes, keep your legs straight and like I said before, just be confident. Those are my tips for doing a back walkover on the beam.