If a user does not uninstall the existing version of Cloud Discovery Tool, then an error is shown with the text: "There has been an error. Cloud Discovery is already installed on this system. The wizard will exit." See the screenshot below.
Follow steps in KB article How to perform uninstallation of Cloud Discovery product from each supported operating system? to uninstall existing version of Cloud Discovery Tool and attempt installation again.
Detailed installation steps are listed in KB article How do I install the Skyfence Cloud Discovery Tool?