FileVault recovery options
If you encrypted the data on your Mac with FileVault encryption, your information is not accessible unless you first log in with your password. When you turn on FileVault encryption, you choose a way that you can unlock your startup disk if you ever forget your login password: either using your iCloud account, or using a recovery key that’s created for you.
Allow my iCloud account to unlock my disk: If you forget your login password in the future, you can reset it by entering your Apple ID and password as you log in.
Note: If you see “Set up my iCloud account to reset my password,” your iCloud account is not set up for recovery. Follow the instructions that appear on screen to set up your iCloud account.
Create a recovery key and do not use my iCloud account: A recovery key is a combination of numbers and letters that you must record and keep track of yourself. You can use this key to unlock your startup disk or disable FileVault. Keep a copy of this key somewhere other than your encrypted startup disk. If you write the key down, be sure to copy the letters and numbers exactly as they’re shown, and keep it somewhere safe that you’ll remember.
If your Mac is part of an organization that has a corporate FileVault account and an administrator configured the encryption settings of your Mac, ask your administrator for help with unlocking your encrypted information and resetting your password.