Add substitute

Hello all, I am working in SRM 4.0 and when I go to approval tab on web transaction and I try to add a substitute, I press this button, then I select active substitution and I put on substitute field value Z* for example, when I click on Find button, system shows me all users for all countries in the company. How can I do to the system shows me only the users that appears in a country? For example in this case only for Spain (this is a company code in my organizational structure)

Thanks

Rosa