So unless I misunderstood your question, you are changing your datasource from Access DB to Oracle DB, correct? Assuming that the database structure remains the same then all you should need to do is go into Database -> Set Datasource Location and set the datasource location from the Access DB to the Oracle DB and your existing report should work as it did. You might have to map some fields, but that should be the extend of it. Is that what you are trying to do?
Chris