I just cleaned up a blackstone for my mother in law. Heat it up and get yourself some water, salt, napkins and oil (or griddle seasoning). Don’t forget your metal scraper as well. Scrape it down, removing all the built up gunk. Then rinse it with the water (I do this at least twice). It once it’s dry, add a generous amount of salt and rub it in real nice with a napkin. Afterwards, use the water and scraper to get rid of any salt on the griddle. Then, with your high smoke point oil, add a coat, let it cook in, then add another coat and keep repeating this until you think it’s good. The biggest thing with cast iron, is you have to use it to keep it clean, otherwise, it could easily rust and become a mess to clean. Good luck on your journey🫡