Answer
Based on Le Chatelier's principle, the buffering capacity of a buffer that has already neutralized a significant acid amount can be replenished if the concentration of the base is increased. This will allow the base's OH- ions to neutralize further of the acid's H+ ions.
Step-by-step explanation
Le Chatelier's principle states that if the equilibrium of a chemical reaction is disturbed by changing the conditions such as pressure, temperature, or concentration of products or reactants, the position of equilibrium shifts to counteract the change to re-establish the equilibrium.
Applying this principle to a buffer that has already neutralized a significant amount of acid, we should increase the base's concentration to re-establish the equilibrium. That will allow OH- ions of the base to neutralize further H+ ions of the acid.