Page History

Open Disk Utility

Go to Macintosh HD

Applications >Utilities>

Disk Utility

in Disk Utility>

Click on the sidebar and choose

>Show All Devices

Pick the drive you want to reformat but choose the 

>External top volume in the display as shown here

Click Erase

Name the Hard Drive

Choose the Volume Format: as APFSName the drive then click

Scheme: GUID Partition Map

Erase in the lower right corner to erase the drive

You can also use 

Format: Mac OS Extended (Journaled)

Scheme: GUID Partition Map

Then Click Erase