I'm afraid that it does happen. Larder units are great, but they're big. They can hold a lot of tins of baked beans, but are easily overloaded.
You need to remove the door first. Then it's a matter of getting at the runners to figure out the problem. It would seem from the instructions, that the door is just clipped into place. According to this manual, you need to prise the door and carriage away from the cabinet. Then you can get at the screws that hold the door clips.
(It looks like the screws are operated by an "Allen key". I can't tell from the photo.)
With the door out of the way, you can easily see how the runners work. These products all seem to be a little different. When you can actually get at everything, it should be obvious how to get everything re-aligned and working.
https://www.manualslib.com/manual/1769780/Kesseb-Hmer-Dispensa-Pantry-Pull-Out.html?page=7#manual