Building an image for r6700 v2

My router is an R6700 v2 that experiences weak signal issue on openwrt. transmission power only goes up to 6dBm max. There is a patch available to fix this issue
do i use diff, mbox, or series?

I think I'm on the right path downloading this file openwrt-imagebuilder-21.02.3-ramips-mt7621.Linux-x86_64.tar.xz

The thing is I'm a noob so I apologize in advance. Don't know what to do next. Do I copy and paste the patch file to somewhere in the file above? any guidance would be appreciated. then use cmd to make image?

You will need the buildroot, not the image builder. The image builder only repackages existing images and allows you to strip or add packages or configuration files e.g..

However, the patch might not be doing anything useful, so I wouldn't try using it yet. See here:

thanks for your reply. You know I actually flashed your image that was posted in another forum on my router.
It fixes the dbm issue and allows it to go up to 20. sadly, though the router power light remains orange and the internet doesn't work so I reverted back to 21.02.3.

I think my router even on stock eventually stopped providing the correct tx but unfortunately i can't go back to stock to check. Nmrp flash always succeeds in flashing stock but then the router just keeps restarting over and over. Only openwrt firmware through nmrp works now

That image contains janh's old patches yes.