Haha, love the old-school question!
But not very clear at all what you are asking.
What do you mean by "put another video inside the face"?
How have you shot the face? Is it on green screen? Can you post any screens shots?
copy and make two layers of this face video. I'd put a garbage mask around the dark half of the face including the hair or not (your choice) Then include the video overlay with experimenting with the Luma effect. If this makes no sense to you then start with the getting started with after effects tutorials
Thank you guys! Will Do!