Install Mojave instead of Catalina
I have an iMac with Catalina 10.15.3. I need to install Mojave so I can do some testing. I have an external 4T hard drive that is connected and it has been erased so it is available. I do not have a time machine backup of Mojave but I did (supposedly) downloaded a Mojave installer from the app store. It is now on my hard drive in the Applications folder. It is called "Install macOS Mojave" and shows 6.05 GB.
I tried following some steps on a MacWorld site for creating a bootable version of Mojave on the external drive but when I got to the steps to enter the command string into the Terminal, it responded that it couldn't find the directory or file.
So, how can I get there from here (i.e. get Mojave installed)? Note, this is all on a separate computer that I'm trading in so I do not need to save any data.
iMac Line (2012 and Later)