If you pick at it or if it infected it won't heal
What Causes A Sore On Lower Leg Not To Heal?
Either poor circulation. Or an infection. If it's an infection you might have to go to the doctor to get an antibiotic. If it's poor circulation I have no idea what they do. Or you could go the easy cheap route and pick the scab and pour hydrogen peroxide on it and cover it with neosporen and a band-aid.
