Install via Cydia Impactor
Cydia Impactor is a GUI tool which can be used to install iOS IPA file without requiring a jailbroken device. Before using this software, please download the latest version of Cydia Impactor for Windows or macOS. You can also download it from its official site: http://www.cydiaimpactor.com/
Step 1: Make sure that you have the latest version of iTunes installed on your computer.
Step 2: Remove the original app from your iDevice.
Step 3: Download and save the IPA you’d like to install, then launch Cydia Impactor.
Step 4: Connect your device to the PC using the USB cable. If everything goes fine, Cydia Impactor should detects your iDevice.
Step 5: Drag and drop the downloaded IPA file onto it.
Step 6: Impactor will asks for your Apple ID username and password which are used to fetch the developer certificate from the Apple servers.
Step 7: Now, please be patient and wait for Impactor to perform all of the work.
Step 8: Once you see the “Complete” message on it, unlock your iPhone screen and go to “Settings->General->Device Management”.
Step 9: Tap the developer Apple ID and trust it.
That’s all. Now you can launch the app on your iPhone.
Errors and Solutions
If you get this error, please go to “Xcode->Revoke Certificates” and revoke the old certificates. Then repeat the installation steps.
This is because there is another version of Pokemon GO app installed on your iDevice. Please remove the original app first and try again then.