The key file is used as an alternative to unlocking/decrypting an encrypted Amber X volume in case you forgot the password.
Note: If you didn't save the key file prior to being locked out, you have to do a factory reset and "Install Other Versions" to recreate the volume again -- meaning you will lose all existing data on the volume. There is no way around a lost decryption password other than starting from scratch. So please be careful protecting your volume decryption password or saving a copy of your volume decryption key file somewhere you can trust.
2. Go to Control Panel, Volume, Export Key File.
3. Enter your encryption password for Amber X. After a moment, the key file will begin to download. You can use this file to decrypt Amber X instead of using the password.