Lay a 6-inch strip of painter's tape vertically along the side of the cabinet where it meets toe kick. The tape protects the cabinet side from nicks from the trimming. Avoid masking tape because it may damage the cabinet's finish.
Thread a piece of painter's tape under the toe kick perpendicular to the extra toe kick piece. This protects the floor from the trimming. Skip this step if the toe kick rests directly on the floor.
Hold a ruler against the side of the cabinet where it hangs over the toe kick. Press the ruler against the toe kick and mark the straight vertical line with a pencil. This gives you a visual of where to cut the excess toe kick.
Use a fine-tooth handsaw to trim away the extra toe kick. Saw down the pencil line and keep the blade close to the side of the cabinet to give you a straight, even cut. Remove the excess piece from the toe kick.
Sand the end of the toe kick with fine grain sandpaper until the end is smooth and even with the cabinet.