To use material you need a global post process volume in your level. Select it and then scroll to the bottom of the details panel to find “Blendables”, click the small + sign and place material into the slot.
A material like would benefit from having a parameter to turn the effect on/off, since adding it to the blendables section will cause it to be always on. A parameter controlled through blueprint would be the ideal way to toggle the effect.
Hope that helps!