There are several things you can do to solve this, you don't have to delete the deck. First, Anki makes automatic backups quite frequently. You can try to import a backup from when you hadn't changed the note type yet. You can also try to simply download the deck again and reimport it without deleting it first. This is normally done when the shared deck has been updated with new cards and you wish to get them. I'm not sure if it will update the existing cards.
The most time-consuming way would be this. Create another profile, download the deck, import it, then export it (the notes) as text. Then switch back to your normal profile and import this text file. You will have to match the fields of the notes to the columns of the file. This kind of import will leave your review history intact - I know because I've done it several times with my decks.
If you encounter any problems, please consult the Anki manual or post on the Anki support forum.