If you're using a crystal reference, then the load capacitance can be set to a value within 6 pF to 30pF range with increments of 0.375 pF. This is done by programming a 6 bit internal register. If a driven reference is used, then this register is set to provide 6pf total (12pf on each leg of the crystal) and since XTALOUT must be left floating, the input cap load in this case, is 12 pF.
The default value in CyClocksRT software where you set this is 18.19pF for a crystal selected as a reference. So you can select a crystal of your desired frequency value (within the range specified) with 18pF load and enter the frequency value (MHz) in the REF entry box provided. You need not provide external caps to match the crystal load.