This is potato ring rot. It is not a big problem. Just soak it in water before eating. If there are potatoes that are too dark, it is best not to eat them.

Extended reading: Potato (scientific name: Solanum? tuberosum, English: potato), Solanaceae Solanaceae, annual herb, also known as potato, ground egg, potato. The earliest artificial cultivation of potatoes can be traced back to southern Peru around 8000 to 5000 BC. Potato, 15-80 cm tall, hairless or sparsely pubescent. The stem is divided into two parts: aboveground stem and underground stem. Potato is one of the five staple foods in China. It has high nutritional value, strong adaptability and large yield. It is the third most important food crop in the world, second only to wheat and corn. Potatoes are grown from tubers and can be used as medicine. They are flat in nature and sweet in taste, and can cure stomachache, ribs, carbuncles and other diseases. As food, its storage period should not be too long and must be stored at low temperature, dry, and airtight. (Note: The sprouts are slightly toxic). There is evidence that the vitamin C content of potatoes is about 4 times that of apples.