Welcome and thanks for posting your query to HCM.
After reading your query I can make out that the flattened forefinger nail is present since 6 months. Now this is quite a long time to grow a normal finger nail. Generally it takes 3-4 months for a finger nail to grow back normally. It appears that the hammer might had hit on the root of the nail because of which the nail is not growing properly. Though we cannot repair the nail root but it would be worth trying to take tables containing "Biotin" and "Iron" in daily schedule for around 2-3 months. Also do take good amount of proteins
in your daily diet
With good health wishes
Dr. Sanjay Kumar Kanodia