Both STL and STEP are fairly common CAD/3D model formats and well supported in many programs so it should be not hard to find one that can perform STL to STEP conversion. Below are few choices that can perform this conversion.
Convert Stereolithography CAD file to ISO-10303 STEP product data.
We found 17 software records in the database related to .stl to .step file format conversion.
Microsoft Windows software - convert stl to step on Windows
A 2D and 3D CAD construction software
Convert from stl file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned stl to step. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A PLM/CAD/CAM/CAE software suite
Autodesk Inventor is modeling application used to create 3D digital prototypes.
3D viewer and converter with huge file type support
A 3D model converter
A family of 2D/3D CAD software products for Windows
A widely-used 3D animation application from Autodesk
A set of 3D modeling tools
Apple macOS / Mac OS X software - convert stl to step on OS X
A 2D/3D CAD software for OS X
Multiplatform software - convert stl to step on any platform
An open source multiplatform 3D CAD/MCAD/CAx/CAE/PLM modeler