"TamilYogi" is not an official app available on standard app stores like Google Play or the Apple App Store. Users searching for an "install" are typically looking for ways to bypass ISP blocks or looking for third-party APKs.
Android
For iOS, the process is a bit different. They need to go to Settings, then General, then Keyboard, add a new keyboard, and select Tamil. They might also need to download an app from the App Store if the built-in Tamil keyboard isn't available. yagavarayinum naa kaakka tamilyogi install