I have reattached the image from my original post, there is a section of the wall covered with stone. That is what I want to achieve. And I have achieved it, I just don't know how I did it since I can't select just that section, it seems to be attached to the wall.
I don't want to change the entire wall material, just a section.
I originally created this in 2018 version and lost my textures, maybe that has something to do with it.
I have attached more images. I have also included the camera view, the texture that I want to change is the stone at the back of the wood storage cavity.