Answer to the question; The trolley only reverses.

The rod with the front wheel and the double rod with handle will be placed in the thick tube. These 2 rods must be exchanged, then the trolley will move forward again. The rod with handle has a gray dot on the rod at the bottom where the rod is clicked into the thick tube. The same dot is also on the rod that is welded to the thick tube. This way you can always see that they belong together.