See
this thread. TL;DR you're going to need cheats or save editing. With cheats, go to the UGC office on Mhen'ga*, then use impulse -> pumpkinStartingQuest. With save editing, set the flag PUMPKING_COMPLETION = 1, though that will skip the introductory scene. Either way, keep a backup in case something goes wrong.
*(the scene(s) that play after automatically punt you through the south exit of the room you're currently in, so it should work in any room with a south exit, but you should probably go to the room you're supposed to be in just to be safe.