You may think, "Wait a minute. My mac is too old and out of the list of supported device to install macOS Mojave!"
I found this and you may give it a try:
You'll need a very good reason and it'd be best if you didn't do it on your main Mac. However, installing Mojave on some older Macs can be done — and fairly easily. AppleInsider explains if you really must know.
The article suggested to download a
macOS Mojave Patcher Tool from
http://dosdude1.com/mojave/