@alisha-- I'm not sure about potatoes, but I have tried apple cider vinegar on scalp warts and it works.
I used the same method that is used on warts that are on other parts of the body. I dipped a clean, rolled piece of cotton in apple cider vinegar and placed it on the wart. It's not easy to keep the cotton on the scalp since you can't put a band aid around it. I kept it in place by putting a headband over it so that the cotton wouldn't move.
I removed and replaced the cotton every day for about four days and the top of the wart become soft and fell off by the end of the fourth day. It basically just disappeared and I didn't get any more scalp warts.
I'm sure adding apple cider vinegar in shampoo or rinsing the scalp with diluted vinegar would help too. But I felt that this method was more aggressive and it probably removed the wart faster this way.