You just need to use a 3D CAD software or web service that lets you import and edit OBJ files on your PC. In this article, you can find some better free tools and software that let you modify OBJ ...

If you check my article on why I use Meshmixer, you will see that this tool allows one to import 3D models in various file formats, like 3MF, OBJ, STL, and AMF.