Do not lose your nerves. Even though you hit someone, it does not mean that that you cannot help him.

Even if you caused the traffic accident, it does not mean that you cannot save the life of the injured.

Do not lose your head.

Call the emergency number 112 (911). Operators will support and advise you how to provide first aid to the injured. 
If it is necessary, the operator will be with you in contact until the arrival of professional rescuers.