If you've already completed the starting house quest (repairs, bed, etc.) just continue with the main story — new scenes unlock new options. For example, once you finish Hannah's route you can cross the bridge. There, in the human settlement, you'll be able to buy swamp ore, which is used to craft ingots. And at another story beat, Marigold will actually send you to the swamp herself. So yeah, just progress the story and it'll open up naturally.