You are unable to install Certo iPhone onto your iPhone or iPad.
Apple imposes several restrictions on what apps are allowed to do on its devices. The most significant being that apps cannot access any files outside of their own container. This means that spyware scanning apps cannot be installed directly onto iOS devices.
Certo iPhone works via your computer meaning it can scan iOS devices for spyware and other security vulnerabilities. Download and install Certo iPhone onto a Windows or Mac computer in order to scan your iPhone/iPad.