After the salt block has fully cooled (and that will take HOURS - seriously!), the best way to clean it is to scrape off all of the excess food particles and then wipe it off with a damp sponge. Don’t use any soap here and since salt is naturally microbial, you won’t have to worry.  Also, don’t soak this in water or run hot water on it. Treat it gently.  You must wait at least 24 hours before you try to use it again to make sure it is 100% dry.