What happens to a reaction at equilibrium when the concentration of the PRODUCTS is increased ?

Equilibrium shift to left, favoring the formation of reactants.

Explanation:

Take the equation below as an instance

CaCO3(s) ⇌CaO(s) + CO2(g)

Once, concentration of the PRODUCTS,

CaO(s) and CO2(g) are increased, the equilibrium constant, K remains the same while the equilibrium position shift to the left, favoring the formation of reactant, CaCO3(s)