How do I set the second identifier in the PID-3 field?

I need to set a 2nd field of a repeated field. For example, how do I set the second identifier for a patient in the PID-3 field? 

There are many ways to handle values in a repeated field. The following sets of code all set the 2 patient identifier to “12345^^^ALT”.

    // set using named fields
    CX cx = pid.PatientIdentifierList_03[2];
    cx.IDNumber_01.Value = "12345";
    cx.AssigningAuthority_04.NamespaceID_01.Value = "ALT";
    // set using the segment
    pid[3,2,1] = "12345";
    pid[3,2,4] = "ALT";
    // set using the message and a fully qualified Path
    message["PID-3[2].1"] = "12345";
    message["PID-3[2].4"] = "ALT";
    // set using the message with explicit SEG, FIELD, REPEAT, COMPONENT, SUBCOMPONENT
    message["PID", 1, 3, 2, 1] = "12345";
    message["PID", 1, 3, 2, 4] = "ALT";