[Freesurfer] How to add volume on pial surface in manual editting the trouble shootings

Dear freesurferers I have faced a problem in editing pial surface in trouble shootings. Since the page https://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/PialEdits has showed how to delete volume which is really useful, however, we faced another problem, that is how to add volume. I selected the edit voxels tool, tried to set Mode to "Clone" (Clone Source to "Aux Volume") and used the middle button on the mouse, but did not see any change on the main volume. The skull strip is fine, so I need not edit the skull strip, but some brain tissue was not included by the red line (represent the pial surface). Could anybody tell me how to add volume on pial surface in manual editting the trouble shootings? Thanks in advance! Jin