Bad news, you are not going to like this (from My Book manual)
CAUTION! The WD Security software uses your password to electronically lock and
unlock your drive. If you forget your password, you will not be able to access the data
that is on your drive or write new data to it. You will have to erase the drive before you can use it again.
The only way in this case to "erase" the password is to format the drive on your computer, and then all data on drive is gone.
People need to keep track of their passwords; a post-it on monitor is one (sloppy) way to do this, but people have too many passwords today for even that.
I suggest you keep all your user names and passwords in a file for each website, device, etc.. If you use Microsoft Word you can password-protect this file. This way you have only one password to remember. Just don't forget that one!!