Step 1. Create SI
The SI can be created either as new (not linked to any single PO) ie. Open SI module>Click the New Button or by copying to SI from one of the PO's in question.
Step 2. Set PO to select PO Items
Click the Items button (1) then set the transaction setting to Copy PO Items (2)
Step 3: Select PO items from one or more PO's
From the dropdown (3) many PO items can be selected from various POs.
Filter the list of PO items by typing the required PO number either using the search field or by simply starting to type (4) after opening the dropdown menu.
Then select the items to be added to the SI by selecting them from the dropdown (5) menu then clicking the add button.