I would say to start by getting a solid bridge kickover and a backbend separately first, and then start slowly combining them. If you have trouble kicking over, use a folded panel mat or something along those lines to push off with your feet. Also stretch your shoulders and back, the closer your hands will be to your feet in your backbend, the easier it will be to kick over (stretch ideas: seal stretch, bridge holds, doing a bridge off your bed/couch, bridge rocks, lifting one foot up from your bridge). Make sure your shoulders are always open and your arms are straight. Doing conditioning on your arms can also help to keep your arms straight while kicking over (handstand holds, push-ups, dips, pull-ups, plank, etc.). Hope this helps!