Apple cider vinegar can work to remove dark spots and all you need to do is take a cotton ball and soak it with some apple cider vinegar and apply the apple cider vinegar to the dark spots a few times per week for at least 10 minutes at a time.
The apple cider vinegar should remove your dark spots fully within a few weeks.
You can also remove the dark spots with lemon juice using cotton balls and same above procedure.