DESCRIPTION

I Haven't seen a thread about this model Repair successfully, 
Here is what I managed to Write my own IMEI With No problem …
You will need to flash T399 (Tmobile USA) Firmware with Odin ….
Here is the Link for the Full Firmware with Custom Recovery 

Flash the Above firmware and Root from TWRP or use Kingo Root ..
Select Model T399 and write your desire IMEI 
Profit?… 

Thanks to Espinoza for providing the Link …

Here is also the Original T399N (MetroPCS USA) Firmware just in case you want to flash back to MetroPCS Firmware ….

Note: If you get No service or searching after you Successfully repair IMEI, Under "Repair" Check "Repair Network" reboot DONE ….

※Please make a backup of your device before installing or updating ROM