Set up a global date field where the user enters or selects the desired date.
Enter find Mode  ---> clear the pause check box in the script step
Set Field [Line Item::Date ; Globals::gDateField ]
Set Field [Line Item::export ; 1 ]
Set Error Capture [on]
Perform Find ---> there is no stored criteria in this step
I am guessing as to which table has the date. If the date is in a related Invoice or Purchase Order table, you can specify that field in the first Set Field Step.