This should go in the Support forum for whatever engine you're using (I'd assume MV but a lot of people - even new people - have one engine shown in their profile but are using another).
Edit: actually I just re-read your title and see you just want the face to animate, so you're not talking about animations from the database, which is what I first assumed. In that case, you're after a plugin.
My More Escape Codes plugin (shipped with the engine - just look for the DLC plugins in the folder with my name) will let you enter escape codes to change the face while a message is being displayed. This will let you change expressions during the message. If you just want them animating the whole time - mouth moving sort of thing, I think there's a different plugin that allows that, but I don't recall what it's called or who wrote it. Look in Plugin Releases or Plugin Requests, near the bottom of the screen.