[HELP] can't flash bootloader and modem G920FXXU2COI5 (G920F)

i want to flash bootloader and modem G920FXXU2COI5 (g920f 5.1.1) but it show error in odin..
is it posible to downgrade bootloader and modem coz my current bootloader and modem is G920FXXU3COI9 (g920f 5.1.1) ...