To use it properly simply sand of the area that has damage until there is no more damage visible (please sand in the direction of wood grain) and then simply apply oil on that area in the same direction of the wood grain.

Let it dry for two days. There is no need to sand and oil the whole peace unless there are other damage.

Also, if the damage is sanded to the raw wood you might want to apply the oil twice (after firs application the area can be bit rough, so the roughness should be polished with used sanding cloth (or even with a dry cloth) and a second oil layer reapplied.