Okal house built in 2001, open roller shutter box

My crank-operated roller blind is stuck and had to be moved with manual assistance the other day; now it is completely stuck!

The roller shutter cover does not show me how it is supposed to work.
Our house is an Okal House ambiente contura c 82 built in 2001.

Unfortunately, I have no idea how to open the roller shutter box. In the attached picture, you can see the crank screwed under the box.
The board is attached upwards with five screws and is inserted at the front of the upper window frame into a plastic angle.

The cover board is wallpapered and goes up to the ceiling (on the left and right you can see the end of the cover board). The wooden ceiling was installed afterwards during construction.

Maybe someone has had the same problem and knows how to open the box with as little damage as possible.

Many thanks and greetings from the Heidelberg Neckar region, Oliver

Ps. I am new to the forum and thank everyone who brings this forum to life.

Hi first of all, you have to first loosen the screw along with the crank. Then you should pull the big flap towards you. WARNING!!!
There could still be screws under the wallpaper. It is best to use a strong magnet and scan.

Thank you for the response I will try as soon as the weather gets better, we have 40cm of snow and it is freezing cold. Regards Oliver

And as it looks, the crank wheel gear is slowly giving up the ghost.