Netgear R7000 Back from Asuswrt to Netgear

Hi all, 

I am at my witsend, i have a R7000 AC1900 which I isntalled Asustwrt-Merlin onto to allow me to use NordVPN.

However this has been very instable and irretatice and i now want to go back to the origneal Netgear firmware.

Where do i fidn the correct files to revert back to Netgear from Asus as wll as the correct process or steps to follow?

Thanks,