Navigate to the Black/Whitelist tab. Select the list which is to be cleared. Click on the [ + ] directly opposite the IMPORT WHITELIST. In the newly opened field below type in a spoof address i.e. email@example.com
Click on the IMPORT button below the field. A second pop-up table appears and you select the ADD + DELETE OLD radio button. Then select the IMPORT option. The list should now only contain the spoof address which you can now easily delete.