Formating PID-3 field

This has reference to the translation from HL7 231 ORU to HL7 231VXU message.

By default PID-3 field is populated with patient id like 686 and I am appending the =MR  to 0(0).PID.#3(0).[4] field. After the translation field will become to 696^^^^MR. since the field is repeatable I have to add patient SSN value from PID-19 field.

The desired format will be 686^^^^MR~541285542^^^^SS

When I assign the SSN value the second value got overwritten. Any help?