The janitor is the first contact person if something in your flat-share is broken, does not work properly or causes you other trouble. He can, for example, give you new light bulbs, install a new toilet lid, screw new knobs on the chairs, etc.. However, this only applies to the furnishings that are provided by the Studierendenwerk!
Below you will find a list of everything you can get from the janitor.
You can find the janitor here