ms8 to mp8 conversion is related to making new projects in old version of NI Multisim (v8). It's actually not file conversion per se, more of using existing designs as a basis for new project. You can only do this with proper version of original software, there is no way around this. But if you have some specific problem or issue with old Multisim files, it would be perhaps best to reach out to Multisim online community or support.
Updated: July 18, 2023