PP-PI - Automatic Value Assignment During Generation

The following help details about automatic value assignment during generation and the scope of generation.

http://help.sap.com/saphelp_47x200/helpdata/en/89/a43836461e11d182b50000e829fbfe/frameset.htm

I need to know where do I enable the scope of generation and prerequisites for that.

For example I have 3 reservation items in process order. I want the item number to be populated in the PI sheet automatically for all the 3 reservation items for goods issues. How do I achieve this.

Regards

Ram