Allow the computer to boot from the USB flash drive.Alternatively, hold the option key and reboot the Mac then use the arrow key to select the USB flash drive as an installer. For T2 security chip supported by 2018 MacBook Pros and iMac Pros, you need to “allow booting from external media” from Startup Security Utility.Backup the entire drive before performing a clean install on your Mac machine.Note: Erase the flash drive to HFS+ (Mac OS Extended (Journaled)) but not APFS. The Terminal creates the installer drive on the opted USB flash drive. Type the administrator password when prompted.Warning: The command erases the flash drive so check there are no stored files backup the files, if they exist, before executing the sudo command. Open Terminal and enter the next command: sudo (drag and drop the installer from application folder to locate its path) –volume (drag and drop the USB flash drive from the Mac volumes to specify its path) –nointeraction –downloadassets.Connect the USB flash drive with at least 8 Gigabytes storage space to your Mac.Locate the installer from the Applications folder (copy it to the desktop if you desire).When the download completes, quit the installer, as it will launch itself automatically.Download macOS Mojave 10.14 from App Store.
