Hi,
I do not advise you to touch the Intel ME (Management Engine) firmware on Z390 chipset, since the Z390 chipset, the firmware must be flashed with the corresponding Intel PMC (Power Management Controller) firmware, for that the ME firmware and the PMC firmware must be packaged according to some parameters via Intel Flash Image Tool to then be flashed with Intel Firmware Update Utility.
I do advise you to let your ME & PMC firmware come with your BIOS to avoid any mishandling (besides there is a new BIOS for your motherboard with a new microcode for your processor :
https://rog.asus.com/forum/showthread.php?105974-BIOS-0602-ROG-Maximus-XI-amp-ROG-Strix-Z390-Gaming).
The interest of flashing a ME firmware manually (what I propose for Z97/X99, Z170/Z270/Z370 & X299 via 3 threads if you search) is especially for people who have a motherboard of previous generations with a old BIOS that does not have the news ME firmware.
Note 1 : No matter which processor is used with the chipset, the ME firmware is the same.
Note 2 : If you want see the ME firmware version that you have, you can see it in the BIOS, Main tab of Advanced Mode (F7).
Note 3 : Do not confuse Intel ME (Management Engine) firmware and Intel MEI (Management Engine Interface) drivers.