Here is what you need to do.
Get the DCD Sprint Carrier cab from
here and transfer it to your device, but don't install yet.
Go to Settings/Connections/Connections/Manage Existing Connections. Tap and hold on the cellular connection. Usually labeled Sprint. Delete the connection.
Install the carrier cab by navigating to the file location with file explorer. Tap on the file and install to the device. Try and open PIE and see if it connects. If not, soft reset and you should be good to go.