SQL Reporting Services - Limited Reporting Control.. How to select first day of Previous Month?

I am trying to run a scheduled, automated report through SQL Reporting Services which will run a monthly report at the beginning of each month using the first day of the previous month as the start date and the last day of the previous month as the last date.

I am trying to configure the report through SQL Reporting Services but only a limited set of criterion fields are available. They are:

All Label                            Date Filter

Aggregation                      Support Group

Classification                    Assigned to User

Time Zone                         TimeZoneName

Start Date Type                Start Date Value

Start Date Offset Type    Start Date Offset Value

End Date Type                  End Date Value

End Date Offset Type      End Date Offset Value

Service                               Queue

I cannot find anywhere the options available for values to enter in the “Start Date Type” or “Start Date Offset Type” fields. I have found the SQL on line to select the “First day of the Previous Month” etc., but cannot determine where to enter this code to make it work with the report automatically. Do I need to open the report through Report Builder V3.0 and enter the SQL query as a default value in one of the parameters? If so, can someone detail the steps or me to do that as I cannot determine how to make that work.