the position of equilibrium will shift to the left.
the general equation for the dissociation of a weak base is
b + h₂o ⇌ bh⁺ + oh⁻
according to le châtelier's principle, when a stress is applied to a system at equilibrium, the system will respond in a way that tends to relieve the stress.
if you apply a stress by adding more bh⁺ or oh⁻, the system will respond by moving in a direction that gets rid of the added ions.
the position of equilibrium will shift to the left, forming more of the undissociated base.