Hi friend, there are two way to downgrade : 
1. try to modify the platform.ini settings (change to 0  Don't check rom file version)
[Bios_Version_Check]
Flag=1
CheckByBios=0
CheckByBiosErrorMessage="This BIOS file is not allow to flash. The flash process will be terminated."
;This flag is the switch of checking BIOS version. 
;Flag              default : 2.
;                        0 : Don't check rom file version.
;                        1 : Check BIOS version.
;                            When rom file version is older then BIOS, it will display
;                              a warning message and close application. 
;                        2 : Depend on BIOS report.
2. Using Intel FPT and flashing a prior version, then adjust it flashing original to align the ME section.
Let me know
Regards
P.S. use this tool run it as Admin and ipload the result file here : 
https://www.mediafire.com/file/4s2lp3ig8...0h.7z/file