Okay, I'm new to blender and I'm making a simple project. I kind of not used to blender's term. Sorry if I'm not using the right terms. How do I keyframe and change a specific polygon on one object to new material in blender. Like this one for example and changing it to
You can use the UV Warp modifier, see Here.
But the simplest way is probably to create all your facial expressions on a big picture, unwrap your object, give it a (Input) Texture Coordinate > (Vector) Mapping > (Texture) Image Texture node chain, and play with the Mapping XYZ location parameters to change the position of the picture on the object:
Another way, probably more convenient, is to use an empty and select it in the Texture Coordinate "Object" output in order to control the image, see answer here: