Case interviews are meant to allow the interviewer to see how you think, how you structure problems, how you react under pressure and a whole list of other aspects that you will need in the real consulting life.
Many times there are no right or wront answers: in the same way as there can be many different answers to a problem, there can be also different approaches to tackle a case. If you think about it in this way, cases just force you to think about things in a structured manner, but they are not difficult per se.
For example, there is no shame of highlighting that you don't have any experience in the specific industry a case is about, but you can still make educated guesses or ask claryfing questions, in order to understand better.
Good luck with your prep!