If you have the Report Generation Toolkit you can use the Qurey Available Printers.vi to get a list of printers configured for your PC, write a vi to select from this list, and pass that printer to the Print Report.vi.
If you don't have the toolkit, you can use the property node (located under the Application Control palette), Printing:Available Printers property to obtain a list of printer names programmatically, then write a vi to select from the list, and pass that printer to the Printing:Default Printer property to set the default printer in LabVIEW programmatically.