Number of chloride satisfying secondary valency in $CoC{l}_3.4N{H}_3$

Primary valency corresponds to the oxidation state of central meta ion whereas secondary valency corresponds to the number of ligands directly attached to central metal ion.
Co has six coordination number. As NH₃ is a neutral ligand, thereby it cannot act as primary valency.
Formula of the complex is $\left[\mathrm{Co}{\left({\mathrm{NH}}_3\right)}_4{\mathrm{Cl}}_2\right]\mathrm{Cl},$ which shows that there are 2 Cl act as secondary valency and one Cl is primary valency.