or better to say how to re-tention it again, if it does not go back. Like this one

Remove the small plastic cap at the upper side of the sunshade frame, you will find a screw to unlock the sunshade. Remove that and pull the system out.

Now you have to find a way to 'block' the sunshade from rotating. In this case some folded paper is used.


Now pull out the small metal pin and 'rewind' the sunshade spring.
Be careful, not too tight, it might break.

Now hold the pin tight and push it back in it's position. That might be the difficult part, because when you loosen your grip before, it will unroll again.
After doing that, you will have a nice new tight fitting. No more loose sunshade.