Files are very useful at this stage. Continue the narrowing of the bridge of the nose downward. Shape out the main lower portion of the nose, shaping around the nostrils a bit at the sides. To define the upper part of each nostril it's almost just a groove in the side of the nose.

Except in the center where it still connects to the lip somewhat, the bottom edge of the nose should be cut sharply back toward the face. The nostril area can be hollowed out slightly underneath to create a shadow, if the structure of the wood remaining to create the nose will support it. The sides and top of the nose slope gently back into the face.

You may want to add some definition around the sides of each nostril, but it looks nice to leave a gentler curve for the small stretch of skin above the nostril, and below the eye/bridge of the nose, that extends from our cheekbone to the center of the nose.