You can only change your birthday once on Facebook.
Facebook allows you to edit your birthday information once during your account setup. After that, you can't change it again. This is a security measure to prevent people from impersonating others or creating fake accounts.
If you need to change your birthday, you can contact Facebook support for assistance. However, they may not be able to change it for you.
It's important to note that your birthday is visible to your friends and other Facebook users. If you're concerned about privacy, you can choose to make your birthday visible only to your friends or hide it completely.
