How to rebuild the skull

It is hard for me,this is the data ,I hope get some help ! I tried to do it, but failed.
nrrd data

Do you mean do you need planning tools for craniosynostosis surgery? Slicer-based method have been developed for this - see details here:

If you just want to do something simple and manual then you can find instructions how to split skull into species:

For manual assembly, I would recommend to use virtual reality, as it makes very easy to position pieces using the controllers: