Use square brackets in thew statement. When you refresh the table, it
will prompt you for a value and give you the option to select a range
and save it (or a value) in the query.

WHERE GlTrans.Period_Date < [ ]

You can also edit parameters from the data menu - Dat,Import External
Data, Paramaters.

If you are using the visual interface to create queries you can enter
the square brackets in the dialog box as the value when you're choosing
criteria.