SolidWorks supports ISO STEP format (.stp, .step) by default, so you can simply re-save the part as .sldprt files. Alternative option is perhaps with 3rd party software which is capable of saving in SolidWorks' formats which, but thight might a little tricky for latest version of SolidWorks formats. However it should definitely be possible to perform a step to sldprt conversion.
Open STEP file Open SLDPRT fileA set of 3D modeling tools
A CAD visualizaton, analyzation and translating system