To be blunt: There is no official "Checkra1n IPA" file that can jailbreak your iPhone directly from the device.
An IPA file is an app format that runs inside the iOS environment. An app simply doesn't have the permissions or the "low-level" access required to trigger a bootrom exploit. Why You Might See "Checkra1n IPA" Online
Some sites offer a "shortcut" that looks like an app icon on your home screen but is actually just a link to a website. This will not jailbreak your phone. The Real Way to Use Checkra1n