In some parts of this mesh, especially on the corners and edges, there are edges that aren't connected. I only discovered it when I tried to sculpt, and this "hole" appeared.
Now, I know that I can fix this manually, and it's not a huge problem here, where I have to deal with just several of these edges. But I want to know if there's any automatic method to connect them, in case I find a spot with thousands of them, or if I already start sculpting and want to fix this after. Mind you, "Merge vertices" or "Merge edges" doesn't work automatically here, because I still need to select and merge each pair of vertices/edges individually. Is there an option, either in Edit mode or Sculpt mode, to kind of "stitch" these kinds of holes? Or better yet, first locate and then stitch them automatically?