Hi,
For a disc that needs an equalisation curve other than RIAA, turn equalisation on, select the relevant curve and, because your turntable already does RIAA equalisation on its own, click the 'Inverse' setting also.
What you are doing is reversing the equalisation applied by the turntable and then reapplying the correct curve for the disc in question.
It can be tricky knowing what the curve should be. Manufacturers at the time tended not to let on what it was.