FOTA is triggered over time. It wont arrive to all users at once , and is intentionally staggered to not overload our servers but also to slow down any potential unknown issues (meaning we may have time to catch it and suspend).
As mentioned in the thread you can download the manual file from our website;
https://www.asus.com/Phone/ZenFone-6-ZS630KL/HelpDesk_Download/Version WW-17.1810.1910.73
Don't unzip it and place the entire single file in your device root folder.
Unplug the usb-cable (if you copy it from your PC)
A triangle will appear in the notification bar informing you that an update file has been found.
Install and then reboot once finished.