Please i need help with root samsung sm-g920a 5.0.2

Hello to all friends,
Please i have samsung sm-g920a from AT&T OF3 with android 5.0.2 i try to root with pingpong.apk but say NOT SUPPORTED YET!
After this i try to root with file in internet with odin NOW phone not work and restart
I download flash from octopus support and see error writing firmware
I want to flash with kies but not have S/N and cannot finf becose phone not work
please any help??