Ford Ka RU8: Request for help with rear bumper construction

Hello, unfortunately on Friday night when turning backwards did not see a bollard and now an ugly long crack in the plastic cover of the bumper (scaffolder) back. Car is a Ford Ka RU8 (built in 2010). A call to the Ford dealer brought disillusionment: for the easy exchange of the plastic part they want 800 euros. As a student for me at all not financially. (especially since the new price was just 6800 euros.) Now I would like to try to get it to r I thought about expanding the bumper, bulging it from the inside and then welding the crack thermally with a soldering iron. I’ve never done anything like this before, but I can’t break it much more. So I can try it just as well. Could someone explain how to get the bumper off? Thank you for your help!