@drw: Thanks! Your hint pointed me in the right direction. Found it, adjusted it, everything is fine!
For anyone with the same problem that any rollers are loose:
First, for adjusting the eccentric screws you need the #10 wrench.
Look for the lower roller. Behind it, there is a long #10 nut which is the eccentric adjustment. Turn it with the wrench until it is fixed. Please check that it's still easy to move the print head.
Uninstall the display first. It's easier to reach the eccentric screws without it. Look under the table from the front. On the right you see two long #10 nuts which are the eccentric adjustment. Turn them with the wrench until the table is fixed and still easy to move.