Bios versions below 3.x have numerous major bugs, as such they are no longer available
if you have a early bios and need to update, you need to install an intermediate release first (v1.20 for the z820 only)
due to the file size i am unable to add the sp61312 file as a attachment to this post, however I did confirm the links are valid as of this posting
the exe link is the actual bios updater, the html link is instructions
https://ftp.hp.com/pub/softpaq/sp61001-61500/sp61312.html