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: Craniosynostosis surgery: workflow based on virtual surgical planning, intraoperative navigation and 3D printed patient-specific guides and templates | Scientific Reports
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:
Hi Andras! I can’t find SlicerVirtualReality extension. Does it belong to a specific version of 3D slicer?