Connect the external hard drive to your Mac
Open Disk Utility
Select the external hard drive from the sidebar
Click Erase
Enter a name for the drive
Choose a format such as APFS, Mac OS Extended, exFAT, or MS-DOS (FAT)
Choose a scheme such as GUID Partition Map if needed
Click Erase to confirm
Wait for the formatting process to complete
Click Done when finished
Eject the drive safely before disconnecting it