How to clear UEFI secure boot keys (or enter Setup Mode) on S1200SPO

I have a S1200SPO with a Xeon E3-1270v6 with versions:

IFWI: S1200SP.86B.BR.64.2017.39.3.01.0729.selfboot

BIOS: S1200SP.86B.03.01.0026.092720170729

I'd like to clear the installed UEFI secure boot keys, which requires entering Setup Mode. I can't seem to enter Setup Mode. Under Boot Maintenance Manager, under secure boot, all I can do is enable or disable secure boot. I'm using the KeyTool.efi (part of efitools) and I can verify that the board is in User Mode, which doesn't allow me to clear the PK.

Is there a way to do this from the BIOS? (maybe a different BIOS version?)

Can I do this somehow by modifying SPI flash directly? I have access to the board and tools to read/write SPI flash.

Thanks,

Josh