Note 5 software problem,can anyone help me?

I have NOTE 5 N920W8

I trIED TO downgrade modem AND flash modem_N920w8_OI1, AFTER SUCCESSFULL ODIN FLASH, I GET "UNKNOWN BASEBAND" with modem_N920w8_OI1.

When I flash stock rom again WITH N920W8VLU2AOK5 then BASEBAND COME AGAIN

how to downgrade MODEM? I NEED TO repair phone, PLEASE GIVE ME ANY SOLUTION