So putting it all together: the user needs a way to get macOS Catalina DMG for a clean install. The correct method is to download it from the App Store if available. If that's not working, maybe they can use the -seed option or a Developer account, but that's complicated. Alternatively, they might need to use a friend's computer to download the installer and transfer it via a USB drive. Also, the DMG is part of the process to create the bootable USB, so explaining the steps from getting the installer to creating the USB would be helpful.