Erase hard drive

Boot into Recovery Mode and use Disk Utility to erase the drive:

About macOS Recovery - Apple Support

If you cannot boot into Recovery Mode use the disks that originally shipped with your Mac and boot holding the "c" key, then use Disk Utility to erase.

you can try to format the drive, delete all the partitions on this drive, or if you want to erase all data on the hard drive completely and prevent anyone from restoring your personal information, you might need to wipe the hard drive permanently.