26 years old. Last year my face skin became dry from under eyes and cheeks. And after one day the dryness became dark spots. Plz suggest any treatment?

Protect. Avoid things that make you break out, soaps ; wetness. Wash your hands only when necessary. Wear gloves when needed. Wear clothes made of cotton. Bathe only with a small amount of mild unscented soap, such as dove. Keep the water temperature cool or warm, not hot! use the medicine your doctor gave you. Use a plain moisturizer daily. Avoid scratching or rubbing the itchy area. Manage stress.
Many options. This sounds likely to be a condition called post-inflammatory hyper pigmentation. Certain laser treatments, prescription skincare or chemical peels can help fade these spots. See an experienced aesthetic skincare specialist, because your ethnicity and skin type is important in choosing the right treatment.