Hi tee4,
The coroplast is held in place by self tapping screws. The best way to remove them is with an impact wrench. You can do it with a socket/ratchet, but that's a lot harder and more likely that the head will be wrenched off the screw.
The rear section of the coroplast is tucked into the drop-frame at its front edge, and into the cap at the rear. So you'll probably have to cut it to gain access. If you do that, you might want to cut a rectangle leaving the front edge intact. That will allow you to bend the coroplast down while working inside. When finished, you can tape it back together using Gorilla Tape or Flashing Tape.