Without seeing it, it may be hard to figure out what needs to be done. There's a multitude of designs of those cabinets.
Close the door and look on the top edge or on the side (at the top) to see if there is some sort of small metal cover, to remove or to open it to access. If there is no access port on the door, look inside the carcass track and see it there is some sort of removable access port.
I would assume the/an access port, of some kind for allowing the removal of the door, would be on the door, itself, on the door's edge, rather than somewhere on the cabinet carcass.
Can you access the dowels in some capacity? One or both of the dowels may be spring loaded. Can you access and depress a dowel to see if it depresses inward, allowing removal from its track?