I gather, you have modded the BIOS but are having issues getting the modded BIOS flashed onto the board, is this correct?
Have you tried SCEWIN to disable the BIOS lock (BLE BIOS Lock Enable) bit/setting? See my guide under point 9.
Alternatively, have you tried using ASUS CrashFree BIOS 3? See page 56 of the board’s user manual. It involves putting the BIOS as “ASUS.CAP” or PZ690P.CAP" onto a flash drive.