Several web-based platforms allow you to upload RFA files and download converted DWG files. Reputable sites like Convertio and Online-Convert offer simple "drag and drop" interfaces that work across all operating systems.
If you do not have Revit installed, several online tools offer CAD conversion services, though their support for the complex RFA format may vary. Convert to DWG
For a need: Use Autodesk Viewer (free, safe, official).