For a Grindr IPA to function correctly on your device, it must be "signed" with a valid certificate recognized by Apple. If you aren't using the App Store, you typically use one of these methods: Install IPA Files on iPhone FOREVER! No Revokes, No Expiry
The user then uses a tool or software to install the IPA file on their iOS device. Popular tools for sideloading include Cydia Impala, AltStore, and Xcode.
Once installed, the user must trust the app by going to the device's settings and allowing the app to run.