I haven’t had time to check the software on my 3D printer, but I have found a workaround.
Just like this post: http://www.vicious1.com/forum/topic/can-these-be-adjusted/
I was able to fix it with a heat gun, and some string.
I tied the center assembly in place, and overstretched it a bit in the opposite direction.
Without it being mounted in the rollers.
Then I heated the area of the four corner bolts, and the long central bolt. (5-7min in total, carefully)
Let it cool down,… and voila