Vapp determination with failure: (from the QRH PER-A 5/6)
VAPP = VREF + DELTA REF + APPR COR
Just get the Vref value (according to your weight) from the Vref table.
You have only 2 options CG aft/forward.
To answer your question, DELTA REF is add to VLS CONF FULL. As shown on the table.
However, I don't understand why they want you to leave CONF FULL on the PERF MCDU?