On the reactant side of the equation the water (#H_2O#) is the Acid as it is the hydrogen ion donor to the bicarbonate (#HCO_3^-#) which is the Base as it receives the hydrogen ion..
On the product side the Carbonic Acid (#H_2CO_3#) is the Conjugate Acid as it is the hydrogen donor to the Conjugate Base (#OH^-#) as it receives the hydrogen ion.
#HCO_3^(-) -> H_2CO_3 # #Base -> Conj A#
The Carbonic Acid (#H_2CO_3#) is the Conjugate Acid pair to the Base bicarbonate (#HCO_3^-#) .
#H_2O -> OH^-# #Acid -> Conj B#
The Hydroxide (#OH^-#) is the Conjugate Base pair to the Water (H_2O#).