[SYS] Form Personalizations - Setting Property Value by Calling a SQL Query

Can be done.

Enter the value as below:

=(SELECT AGENT_ID FROM PO_HEADERS_ALL WHERE SEGMENT1=:RCV_TRANSACTION.PO_NUMBER)

:RCV_TRANSACTION.PO_NUMBER is a Target Object ("Item" Type) name, which you can refer after you clicked on "Insert Item Value..." button. It can also be found under Target ObjectLOV with Object Type "Item".