Having created the object representing the external routine and attached it to entity your_routine, you may now call the routine with arbitrary actual arguments through the procedure call, a feature of class DLL_32_ROUTINE.
The procedure takes a single argument, of type ARRAY [ANY], containing the successive actual arguments to be passed to the external routine. The easiest technique is to use a manifest array, as in:
your_routine.call (<<-325, 67.2, x, a+b>>)