FileVault recovery options
If you encrypt 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 with the Apple ID you use for iCloud or with 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”, you haven’t set up iCloud for recovery. Follow the instructions that appear on-screen to set up iCloud.
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 turn off 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 organisation 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.