Close Rear First
I'm bor425 not sunny. I was able to fix my roof based on Sunny's instructions. Before you start you have to get the rear panel closed first. Otherwise you can not slide backward the front panel either. The rear panel can be closed (also in the instructions) using a screw driver and push back the two ramp fittings inside under the rear glass, each time left and right a little (1cm), you may have to use some force to get them going but not to much.
Once the rear is closed you should be able to push back the button which should slide back the front panel. That worked for me and then I was able to continue with Sunny's intructions standing in that back of the car and having a good top down view through the open window. However if the front panel does not open there might be an other problem. I have no experience with that.