This application requires iOS 12.0 or later

Which iPhone do you have? You can check to see if it will update to iOS 12.0 or higher by opening Settings > General > Software Update. The following screen will tell you which iOS version you are on and whether your iPhone can be updated any higher.

iPhone model 5c cannot support iOS version beyond 10.3.3.

If your unidentified iPhone model cannot run iOS 12 or later, there's no way to download/install that app, sorry.

Regards

Giulio