Reset Android: If you truly need the app, you can factory reset the device, making a backup of any data that will be lost in the process. Of course, think carefully if it's worth it, because the 'Application not installed' issue may reappearance at any time.

Avoid that app: one of the causes for 'Application not installed' failure is that it contains a programming fault, which the system rejects. So, check the Internet to see if there are any complaints from other users, because using that programme may not be convenient for you.