One of my questions that I recently asked was put on hold because it would be better on the World Building SE, so how do I migrate it there?
You can flag to ask for migration, or you can just re-ask the question on the other site. If the question already has answers, in particular (as yours does), then those answers might not work on the other site, so moderators would have to evaluate that. Also, you might need to adjust your question to fit another site, either content or tags. That might not be a big task, but at that point you might as well ask the edited question directly on the other site instead of waiting for moderators to see your flag. Re-asking seems easier for an experienced user (you already know how to go there, read their tour/help, copy your post source for use there, etc).
Flag it for a moderator - if they think the question would indeed be a good fit for the target SE, they'll migrate it.