If you need to defrost a frozen car door lock there are a few things to try.
Use a blow dryer to heat the lock area and the seam of the door. Heat up the key with your hand to see if a warm key will turn the lock. Alternate lightly pushing and pulling the door to break the ice seal that may be affecting the lock.
If you still can't get in don't force it. Get help from a professional locksmith company for assistance to avoid damage to the seal in the door and to get into your car.