UE4 reset materials of an object to default

Hello, everyone. I have just tried putting a livestream into a plane and planned to take the green color off. However, when I tried with MF_Chromakeyer function in the material, the scene of plane is entirely too transparent. I doubt that the materials of plane is in a mess. So I would like to know the way to resetting materials to the original state or clear them all to have a new scene. Thank everybody with your help.

Right now not only does the simple green screen is too transparent, but composure is so shining after having a garbage matte in front of the virtual camera. Hope everyone could have me with this problem. Thank you very much!

Try this.