As you can see in the image, I attempted to cut the area shown in red lines (which are diagonal) and fill it with white so only the bottom part with the green lines are seen. I:
1: Tried the crop tool and making a preset (but the area was rectangular and there was no option for diagonal or straight areas.
2: Tried shaping the eraser to a diagonal line which resulted in imperfect cuts.
3:Tried to paint the whole place but failed.
So is there a way for me to perfectly crop the image so that the only visible part is the bottom?