This is hopefully a real rare issue to run into, but you never know. You just might be a klutz too.
I was working on a site for a client when I realized I mislabeled the custom post type I created. I already had a bunch of content for that custom post type, so when I renamed the CPT all those pages disappeared of course. They were still attached to the old post_type.
They are still in the database though and here’s how you can quickly update them without having to manually change the post_type field for each entry.
You’ll just need to login to phpMyAdmin and run the following SQL query after changing “old” and “new” in the query.