create defected area

Operating system: windows
Slicer version: slicer 4.8.1
Expected behavior:
Actual behavior:
I can’t create a missing area of ​​a skullcap,
I watch a tutorial on you tube but it refers to a very previous version and there are not the same tasks

I would recommend to use latest nightly version of Slicer and these tutorials: https://www.slicer.org/wiki/Documentation/Nightly/Training#Slicer4_Image_Segmentation