1. Go to "recovery mode" (Bixby+VolumenUp+Power buttons, pressed at the same time until blue screen appears)
2. In the recovery mode screen choose "wipe data/ factory reset". (after that, you will be in the recovery mode screen again)
3.In the recovery mode screen choose "Reboot to bootloader"... (this option will bring your phone to "download mode"
4. Connect your phone to your computer and open Odin PrinceComsy.
5. Choose the file "ENG_ROOT_N950U" clicking on AP option on Odin.
6. After that the phone will restart normally after the "serial number screen" appears
7. Now you can unlock your phone on z3x box choosing G935P model .
8. After unlock, flash it with original firmware. You can find Samsung original firmware here, Samsung Firmware Updates
source: gsmforum