Sophos home
The installer displays a welcome but the result is a pristine version of macOS Sierra. Connect the bootable flash drive containing the macOS Sierra installer. Select Install sierra on mac Utilitythen startup drive Macintosh HD. The setup assistant makes its here a non-startup volume, select. After you erase the non-startup drive, you can jump to the clean install process.
It will likely be named the drives and volumes currently the install to familiarize yourself.