As of Release 3.0, you will find a new function under Goods receipt for purchase order - PO number unknown.
On the initial screen for this function, you can enter the following search criteria for purchase orders or shipping notifications:
You can find out more about individual fields and search options in the field documentation.
Furthermore, you can still search for the purchase order according to the above criteria using the function "Goods receipt for purchase order - PO number known".
From the function "Goods receipt for purchase order - PO number unknown", you can switch to the function "PO number known".