Dear Zahid,
How do I upload firmware to my NETGEAR router using a TFTP client on Microsoft Windows
hnyman directions below :
R7800 has an easy-to-use TFTP recovery mode
Quite similar process as e.g. WNDR3700, which is documented in the Openwrt wiki:
Click on the links above and read carefully and you should be good to go
It is all well documented and pretty straight forward of a process
You can use this method to flash OEM firmware and OpenWRT factory images
If you wish to use sysupgrade.bin - then you can flash this through Luci
You can look that up or someone will help you out with that
I always use Philippe Jounin Tftpd64 in order to revert to OEM stock firmware and then flash fresh OpenWRT factory.img