Just recolour it to match with the background. Also, the watermark is there to show you who it belonged to, so instead of removing it, just let it be. You're discrediting the owner. Or maybe if it's from a pirated site, which means you should use the official one when you're profiting from it. That aside, what manga is it?
Watermarks are designed to be hard to remove. The easiest way would be to use softwares dedicated to removing watermarks.
It's a pirating site.. and i'm not profiting from it at all. i am not skilled enough so i guess i'll just leave it.. the name is 'okashina tensei saikyou patchie isekai korin' i'll practice, thanks. blame them for not making it english! ooooh, alpha!
It's actually patishie, if you copy paste what you wrote and Google it, you gonna be confused for a solid 5 minutes
what chapter are you on? http://isekairaw.com/manga/okashina-tensei-saikyou-patishie-isekai-korin-raw/chapter-7-1/ this has the raws up to ch7.