Sorry, this is going to be confusing. I swapped from a Netgear WNDR3700v4 to a R7800 because the WNDR3700v4 wasn't mine and wasn't supposed to be modified with openwrt, once family found out i did this, they wanted me to revert to oem factory firmware. I fixed the issue with not being able to renumber the address to what i'd like it to be by simply going to modem to change it to a different i believe "subnet" or "octet", used it for couple days and then had to revert back to oem firmware.
I'm new to OpenWrt and reason i didn't go with the renumbering method by commands is because i'm not fluent with how to do it and easier just to go by GUI but GUI doesn't seem to work and always goes offline/reverts after 30 seconds.
Today i received mail for the NETGEAR R7800 i purchased online. Better than the older router my family had which was a single core and less RAM too.
Sorry, what i mean by "fix was to go to CMD to change it manually rather than from GUI" is because others stated this. I can't even find the article on reddit at the moment. Don't know what i was doing on Google search to find that. My way of doing it was to change it from my modem from 192.168.1.254 to 192.168.2.254 and it finally worked, i can access both modem and router gateway addresses and configure both without issues. If i can find it i'll post it here, lleachii.
Here's two of them: