Locating Your Device’s Identifier
Locate a device’s identifier to register it as a development device using Member Center.
For iOS apps, connect your device to your Mac.
In the Devices organizer under Devices, select your device.
Select and copy the text in the Identifier field.
Xcode automatically registers a connected device that is enabled for development. But if you are registering multiple devices for development or testing using Member Center, you need to locate the device IDs or use iPhone Configuration Utility to create a devices file for you.