Sketchup is not very flexible when it comes to files you can save the models as. The only thing I can think of is to see if there is an export option of some sort in the drop down for saving the models. Step would be ideal. However, it is unlikely there will be any file type that will be able to work with solidworks from sketchup.
I've imported sketchup files to Keyshot, and then exported those to SolidWorks.
The results are good, but Sketchup files look to essentially be STL files, so once it is in SolidWorks the data is somewhat useless. Flat planes are composed of several triangles. A curve can be composed of hundreds or thousands of triangles.
You could use something like Design X to basically recreate the part sketch by sketch, and feature by feature.
Or you could simply wrap a surface over the mesh, and export it to SolidWorks.
The method used will depend on the end goal and the complexity of the part. Converting a mesh model to a parametric, or clean NURBS body is difficult.
Sketchup file your can work with 3d max maya or AutoCad - soldworks some times need more info how get