How to add Company Code to the Standard Transaction KP90

Requirement:

I have copied the Standard transaction program KP90 to 'Z' program, Now how do I add the Company Code to the Selection Screen of KP90 transaction.

Where exactly do I need to make the change in copied 'Z' PROGRAM. I am not using any user exit concept, as I have already said, I have copied KP90 Transaction to Z PROGRAM. I need to add the company code to the Z PROGRAM. I am not understanding where exactly to add the code.

Please help me out.