You're looking for the BIOS bin file for the HP EliteBook 840 G5.
How to Obtain the BIOS Bin File for HP EliteBook 840 G5:
Open the original corrupted backup (which has your correct DMI) and the new bin file in HxD. Copy the DMI region from offset 0x300000 to 0x310000 (varies by version) into the new bin, then re-flash.
Alternatively, use the HP BIOS Update and Recovery utility (included in the SoftPaq) to "Create Recovery USB flash drive." This process copies the necessary .bin files directly to the USB drive's HEWLETT-PACKARD\BIOS\New folder. Critical Version Notes