what if the device is not showing up in list of devices
all of my devices do not show up when I go to manage devices. how do i add them?
iOS 6.1.4
If you use iTunes Match on the device, enable automatic downloads on it (Settings > iTunes & App Stores on iOS 6 devices) or re-download past purchases on it should link a device to an account (that I'm not sure that it always happens). As far as I can see doing so doesn't really gain you much though, apart from stopping it being used with another account for 90 days