sldprt to 3dxml conversion is in most cases sought by users looking for a way to export SolidWorks content, in this case CAD parts (.sldprt) to the 3DXML format used in Dassault Systemes software (CATIA / SIMULIA etc.).
This might actually be a little difficult, considering 3DXML format is proprietary and as such not really commonly supported. Your best option to how proceed is to export the SolidWorks file to exchange format that can be imported to software featuring 3DXML format support. FBX is popular choice for this, but you can certainly find other alternatives.
Updated: September 21, 2023