You will need to keep it warm and feed it warm kitten milk replacer (e.g. PetLac) from a dropper every two hours. You can buy the kitten milk replacer and dropper from a pet shop.
You will also need to wipe its bottom with a damp tissue (after it has drunk the milk) to encourage it to urinate.
Wipe its eyes with a warm damp cloth, gently passing the cloth from the top of its closed eyes to the bottom. Do not try to open her eyes – they will slowly open on their own in a few days or so. When they do, just clean them the same way.
After cleaning its eyes, use the cloth (without wetting it) to wipe over its body , top and underside, around its head, chin, neck and behind its ears and along the tail. This is like giving a baby a massage and the kitten will love it!