Convex hull was just suggested as an initial step.
There are lots of tools in Segment Editor. If the holes are small then you can fill them using Smoothing effect - “Closing (fill holes)” method. You can also go full manual and fill the holes using Paint or Draw effects.
I Installed a recent version and now I have access to brush option. when I choose smoothing and then brush option,Median smoothing method and finally kernel size of 5mm, the effect make hole instead of filling hole!!! In the video you sent it works correct and fills the holes. what is wrong with me?
Median means that each voxel is replaced by the median value of its neighborhood. Therefore, it can add or remove points - whatever makes the region smoother. If you want to fill holes, choose the fill holes option.