I forgot the password of the external hard drive
If the drive was locked with BitLocker or a brand security tool you cannot open it without the password or recovery key. Please check your email notes cloud or any printouts where you might have saved that key. If you cannot find it the only option is to erase and set up the drive again which will remove all data.
If the drive is BitLocker-protected, then you cannot access it without entering the correct password.
In order to access the drive again without having a password, format it. But this will lead to data loss.