Hi Leigh, open up the handles so the edges of the blades are exposed and run the file a few times up and down the edge at the same angle as the original, normally about 30 degrees. Wear gloves as a precaution in case to prevent cutting yourself on the freshly sharpened edge.  You should see a bright new metal surface from the diamond file – if you have any deeper gouges these may take a bit longer to remove using the same technique.