Use the Asus Firmware Restoration/Recovery tool available on their website for every product...it's the only way to upload the Fork firmware after using the official version. Just look around for the howto as it's pretty easy. https://www.asus.com/ca-en/Networking/RTN16/HelpDesk_Download/
When I try using Asus Firmware Restoration/Recovery tool (doesn't work at all in my Windows 10 desktop -- Works on my old Windows XP laptop) I can only get to 58% at Max. firmware install progress before the utility says device isn't in rescue mode.
at cmd prompt entering ping 192.168.1.1 -t I can see that my N16 is in rescue mode for a few seconds [TTL=100] then it goes to [request timed out] then to [TTL=64]
something has changed, because at command prompt (before the successful installation of the stock firmware) the router would/could stay in Rescue mode literally for hours.