erase an encrypted password locked disc with forgotten password

Is the drive using hardware or software based encryption? If it is hardware based encryption check the proprietary software for any settings or options, otherwise you will need to contact the drive manufacturer for assistance to see if there is any way to reset the drive (this will lose all the data on the drive). Some types of hardware based encryption have no way to reset the hardware if the password or recovery key is lost.

If the drive is using software based encryption, then the link @BDAqua provided should do the trick.

Depends, it may not be possible.

https://support.apple.com/en-us/HT208496