Employ The RICE Treatment
When the black toenail is the result of injury, it will typically resolve without needing treatment, though affected individuals can employ the RICE (rest, ice, compression, and elevation) treatment to help the injury heal faster. Black toenails caused by injuries are the result of broken blood vessels. After the nail grows out, the spot will disappear. If the spot doesn't go away after the nail grows out, there may be a different underlying cause.
Affected individuals shouldn't overwork their injured foot. If possible, they should keep pressure off it and try not to walk. Using ice can help because it numbs nerve endings and reduces both inflammation and swelling, and compression keeps the foot from becoming swollen due to fluid gathering around the injury. Finally, elevating the affected foot higher than the hips helps increase blood circulation and promote faster healing.