@infratech 

In case you are rarely entering the setup GUI, but feel like that watermark is bugging you a lot when you do, then you could maybe consider disabling that watermark image temporarily each time.

If you use the Chrome browser or the Chrome-based Edge browser on a PC, then log into the router's web GUI -> position your mouse cursor near the far left or far right of the watermark image (basically a place where the watermark image isn't overlayed by other html stuff) -> click the right mouse button -> from the pop-up menu select "Inspect" -> the DevTools window will open and in the lower part of it you can see the line "background:>url(.../tp-beta-mark...png)..." -> hover your mouse cursor over that line and a checkbox will appear in front of that line -> uncheck the checkbox and the watermark image disappears -> close the DevTools windows by clicking the "x".

Of course, clicking the "Reload" button of the browser or re-opening the router's webpage will bring the watermark back.

@woozle I need a permanent solution. Any way to access the firmware and jst change the image file or simply edit the image and replace.