Maria is right. When you Save the output screen and come back to the Selection screen and press F6, your saved versions are listed from where you can select one. Just like a layout/variant. And then this field appears. This field will be greyed only. You can select different values through F6 only. Paul is right in suggesting to try F6 key.
See initially I did not have the field. Now I got it. After saving the first Output layout.
