how to install mojave onto erased hard drive

Build a bootable installer on another Mac running Mojave or earlier (and that other Mac must be supported by Mojave) and transfer that installer to this Mac and boot and install from that, or install the oldest macOS version supported by this current Mac using Recovery and then upgrade to Mojave. A few Macs did top out at Mojave, and those Macs can have Mojave installed directly from current-version Recovery.

You need first acquire the Mojave installer.

How to upgrade to macOS Mojave - Apple Support

Downloading that from Apple usually requires a system running Mojave or earlier.

Then to create the installer:

How to create a bootable installer for macOS - Apple Support

it tells me my hard drive doesn't meet the requirements ? is this because it already has mojave on it??

It could be. While Mojave converts the file system to ASFS, reports here indicated it wanted to install on an HFS+ file system to start. I don't think that was a widespread problem, but it seemed to solve some install problems by erasing and formatting Mac OS Extended (Journaled).

You install an app called a virtual machine app. The app then runs. Within the context of that app, you can then install and run what are known as “guests”; guest operating systems. Guests for Mac hardware can include Mojave.

Within the Mojave guest, you can then run that abandoned app, pending app upgrade or app replacement.

Your app then runs on Mojave and usually entirely as it always has, though within the context of the virtual machine and its guest operating system.

This then allows you to isolate and run the deprecated and abandoned apps, while the rest of your apps can be kept current.

VMware Fusion and Parallels Desktop are two of the available commercial examples of virtual machines available for macOS, and there are others.

Maybe acquiring some local software support assistance or consulting here might be of assistance?

ps: More generally, beware asking very pointed questions. Such as how to resolve a particular sequence or a reinstallation problem or how to downgrade. Including some “here’s why I’m trying this path” background can be a helpful approach, as it opens up the discussion a little. It allows options. Pointed questions can sometimes be a very problematic approach, as it can get you a correct answer for the direct question, but can also easily miss potentially better alternative answers.

brianmadden59 Said:

"that is what i am trying but doesn't work for me I am guessing the installer is not in my Applications folder?"

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USB Bootable Installers:

Go Here: How to Create a Bootable Installer for macOS - Apple Support

First, Create the USB Bootable Installer, and then Use the USB Bootable Installer.

1. Create the Installer:

You would create one on a Mac. If you have no access to this, then use another ac that you have, or someone else's (friend, coworker, family member, peer, etc). Of course, ask them permission before you use it. :)

So, start by inserting a USB Flash Drive of 16GB into the Mac and then enter this Terminal command for Mojave:

sudo /Applications/Install\ macOS\ Mojave.app/Contents/Resources/createinstallmedia --volume /Volumes/MyVolume

and then...

2. Use the Installer:

Once created, follow the steps in the above link on how to use it (How to Create a Bootable Installer for macOS - Apple Support).

If you do not have the Install macOS Mojave app in your Application folder, the rest of this won't work.

You must acquire and download the installer first.

You will need to download the installer from the Mac App Store.

And getting that download from the Mac App Sture usually requires you to be on a Mac that can run Mojave, and that is presently running Mojave or earlier.

Which models of Mac do you have?

Which years?

Which versions of macOS are these Macs running?

What happened to lead you to try to re-install Mojave?

Your apps are toast. You may still need them and there are many others with similarly abandoned apps, and I have some that were abandoned at High Sierra, but the app vendor has walked. Which means you’re working toward though seeking to delay an app migration. One way to delay that app migration while still moving forward is to run Catalina, and to boot and run Mojave as a guest of Catalina, and run your apps on Mojave, pending migration to supported apps. This involves adding a virtual machine to Catalina, and which can then allow you to install and run Mojave and Mojave-dependent apps as a guest. This also contains your requirements fir these apps, allowing the rest of your environment to move forward, and providing a platform for whatever apps might replace this abandonware.

Well, is the installer in your Applications folder? It'll be named Install macOS Mojave, if it's there.

Usual path for Catalina and the 64-bit migration is updating the problem apps, or replacing the apps, or running the old apps in an installed macOS guest in a virtual machine pending replacement.