External drives · Passwords and encryption
What happens if I forget the password to my encrypted external drive?
Short answer: Without the password the drive's data can't be read by anyone, Apple included. Check Keychain Access and the password hint first; if it's truly lost, the only option is to erase the drive and restore your files from a backup.
Without the password, the data on an encrypted drive can't be read — by you, by Apple or by anyone else. That's the point of encryption, so there's no reset button. Check first whether your Mac saved it: open Keychain Access and search for the drive's name, or use the password hint macOS shows when you try to unlock it.
If the password is truly lost, the only way to use the drive again is to erase it in Disk Utility, which deletes everything on it. Restore your files from a backup afterwards.
To avoid this, store drive passwords in your password manager or keychain when you create them — see how to stop a drive asking every time.