If you have the installer in your Applications folder, you can create a clean ISO using Terminal:
If you are already on an older version of macOS, check System Preferences > Software Update to see if Catalina is available as an upgrade. Macos Catalina 10.15.7 Iso Download --39-LINK--39-
👉 [Replace this hyperlink with your --39-LINK--39- if it points to a legitimate guide or tool; otherwise, keep the Apple link here.] If you have the installer in your Applications