When you just change your password the passkey isn't changing (Maybe, it's a bug?). So, how to change it?
Right. There is a bug (filed here) that changing your password while your encrypted home directory is mounted doesn't also change the encryption password of that encrypted directory. (It's possible that's by design for security.)
But you should still have the command if you want to change the password of your partition. Assuming your password has already changed (hence the issue), first mount the drive with your old password:
Then re-wrap the password with your new one:
If you are locked out of your system, press Ctrl+Alt+F1 at the lock screen for the
TTY (full-screen terminal) and login there to run these commands.