after that, the installation process is complete so follow the steps on pictorial for installation. You can download VirtualBox latest version from the link which I have given on the requirements, and install that on your computer. The time that files requirement is downloaded successfully the file is completely compressed by Winrar, so you can use Winrar or 7Zip, in this case, you need to download the Winrar software for your computer and install that after installation, Extract the file of macOS High Sierra.
Have a clean installation of macOS Mojave on Virtualbox.Virtual Machine settings for macOS High Sierra.Create a New Virtual Machine for macOS High Sierra.Extract macOS High Sierra from the compressed file.
System Requirements to install macOS High Sierra?.