Sand the damaged area and area around it with medium-grit sandpaper to prepare the surface for repair.
Press the point of a scratch awl about an 1/8th of an inch deep in several spots into the area surrounding the damage and inside the damaged area. These holes created by the awl's tip will provide a surface for the filler to adhere.
Mix up a small amount of high-performance wood filler. Add a small dot of the hardener from the tube provided with the filler to a small amount of filler. Generally, a dot the size of a pencil eraser for the filler is enough for a half-dollar size dab of filler. Mix the two with a putty knife.
Fill the damaged area of the desk with the mixed filler using a putty knife to pack it into the area and shape it to the desk's surface. Allow the filler to dry for about one hour.
Sand the filler with medium-grit sandpaper until it is almost flush with the desk's surface. Continue sanding with fine-grit sandpaper until the filler is flush with the desk's surface.
Wipe the repaired area of the desk down with a tack cloth to remove any dust from sanding. Touch up the repair with a matching touch-up finish. Allow the finish to dry for 72 hours before using the desk.