May I note that this same jumper exists on multiple other workstations and thus this method may apply to others. For example, the Z420 and Z620 are built on the same motherboard PCB with only small differences. In the pic below #37 is the Flash Override jumper position. Jumper at #38 is the Password clear jumper. A third undocumente important jumper is between the bottom two PCI(e) slots (23-24) in this diagram. That is the Crisis Recovery jumper that finally was documented best by HP when there was a rash of BIOS corruption that in some cases could be fixed by the method described for the ZX40 and earlier generation workstations, and also detailed in our long-running post in this forum. Here is the HP link, and the picture below that:
https://support.hp.com/us-en/document/c05163478
Finally, there is a link HERE to a thread in the forum here on the HP method of using the FO jumper in the Z820 to enable updating the ME firmware. Dan_WGBU is a HP engineer who has provided valuable insight from within HP on some of these more obscure procedures. There are critical steps he provides in that archived post.