According to werner theory primary, secondary and duel valency of central atom in  Pt(en)2(H2O)ClCl3 Complex respectively

4Cl- satisfies primary valency,  H2O and 2 en (bidentate)satisfies secondary valency and the ligand satisfy primary and secondary valency is called duel valency, that means ligand involved in calculation of primary and secondary valency. Hence   Cl-  ligand acts as primary and secondary valency in given complex Pt(en)2(H2O)2Cl4 , so duel valency  of Pt(en)2(H2O)2Cl4 Complex is 1