See the official documentation:
http://docwiki.embarcadero.com/RADStudio/XE8/en/Running_Your_iOS_Application_on_an_iOS_Device
Steps to Run Your App on an iOS Device
Connect your iOS device to your Mac with an Apple USB cable
Run the Platform Assistant on the Mac.
Test the connection to your Mac (on the Connection Profile Manager page).
Connect an iOS device (such as an iPhone or an iPad) to your Mac using the Apple standard USB cable (illustrated on the right).
Note: Your iOS SDK version does not need to match the iOS device version. You can use the latest version of the iOS SDK and run your application on older iOS versions that RAD Studio supports. You should always use the latest version of the iOS SDK version.
In RAD Studio:
In the Project Manager, expand the Target Platforms node and double-click the iOS device target platform that matches the architecture of your device, either iOS Device - 32 bit or iOS Device - 64 bit. The selected target platform is displayed using a bold font.
In the Target Platforms node, expand the selected iOS device node, expand the Configuration node, and double-click the Development platform configuration to select it. The selected platform configuration is displayed using a bold font.
Note: You cannot run applications directly from RAD Studio into an iOS device if you build them with the Ad hoc or the Application Store platform configurations. To run applications deployed for ad hoc distribution, see Deploying Your iOS Application for Ad hoc Distribution. To run apps built for the App Store, you must submit them to the App Store and install them from the store.
Run your app, either with debugging (Run > Run) or without debugging (Run > Run Without Debugging).
RAD Studio builds your app using the SDK that you previously added to the IDE, connects to your Mac using the connection profile that you configured for the selected iOS device target platform, and the Platform Assistant on the Mac launches your application on the connected iOS device.
Notes:
The first time that you use a user account on your Mac to run an application on an iOS device, your Mac will prompt you to allow RAD Studio to sign applications using your private key. You must accept this on your Mac so that RAD Studio can continue running your application on your iOS device.
RAD Studio might look frozen at some points until it launches your app on your iOS device, but it is just preparing to run your app.