Fully open the microwave door.
Hold the vent grille straight. Tilt it slightly forward.
Insert the bottom of the grille into the top of the microwave opening over the vent. A few clasps or tabs are usually located at the bottom of the grille. They should connect into the microwave underneath the vent. Line them up with the openings below the vent until the grille snaps into place.
Insert the screws into the pre-drilled holes on the top of the grille cover. Tighten the screws.
Close the microwave's door.