You are assuming it has an accessible service menu. I would not.
If your manual is of no help, and there is no help on the monitor's webpage, and you cannot access such a menu via the OSD menu, then you likely are out of luck. Some monitors only allow access via a proprietary service cable connection. But without the cable, or their proprietary software for such purposes, you are out of luck.
I have to ask, why do you want to edit the EDID? Typically, if there is an error, this is corrected by the maker who flashes the EEPROM, or by the maker releasing an updated .inf file that updates everything.