Locating a Device Identifier
Locate a device’s identifier which you'll use to register the device for development with Member Center.
For iOS and tvOS apps, connect a device to your Mac. For watchOS apps, connect an iPhone paired to an Apple Watch.
In the Devices window under Devices, select your device.
The device identifier appears in the Identifier field.
If you are registering multiple devices for development with Member Center, you need to locate the device IDs for each device and can bulk upload them to Member Center, as described in Registering Multiple Devices.