Vitamin D can help with a cold virus but Vitamin D cannot cure a cold virus.
There's no cure for the common cold however taking Vitamin D can help prevent the onset of the cold virus.
When you have a cold virus all you can do is take some cold medicine, drink tea with honey, stay hydrated, get plenty of rest, keep your room moisturized with a humidifier or vaporizer or boil a pot of water to get some steam in the room.
Taking a steamy hot shower can also help with a cold especially if you're congested.