Springs currently available in PrePoMax are spring to ground elements so they can be used only to connect a point or surface to “ground”. To apply force via spring (if that’s what you want to do), you would need two node spring elements. For now, they have to be added via Keyword Editor: Spring between two nodes
Otherwise, to make force vary with the solution (displacement), you would need CalculiX Fortran subroutines and this is really complicated.