How to Change Birthday?
Step 3: Scroll down and click Edit next to Birth Date or Birth Year (you’ll need to hover over the info you want to edit for the Edit option to appear)
Step 4: Use the dropdown menus to change your birthday
Step 5: Click Save Changes
You can change who can see your birthday by adjusting the audience. There are 2 audience selectors next to your birthday: one for the day and month and one for the year. Friends won’t get a notification about your upcoming birthday if you don’t share the day and month with them.
Why you can’t change your birthday?
They require everyone using Facebook to provide their authentic name and birthday, so you always know who you’re connecting with. Because of this, you can only change your birthday a limited number of times. If you recently changed your birthday, you may have to wait a few days before you can change it again, even if you haven’t reached the maximum number of birthday changes yet.