I ended up with just one last corner which is not oriented properly as shown in the picture. I cannot seem to solve it using R’ D’ R D algorithm, it messes up the whole square when the corner piece gets oriented. Every time I try to solve the cube, it again has just one last corner disoriented. None of the algorithms mention one last corner case. they always talk about 2 or more corners disoriented. I don't understand. Can someone explain whats happening and how to solve it?
You can't. Your cube is in an unsolvable state. You must take apart the cube and fix the corner. This happened because one piece was put in improperly. You can either flip one other piece or flip the disoriented piece