in sketchup 2017 or 2018 you have to go in window then go to extensions manager and clik on install extention
learn How to import .obj 3d files in SketchUp.
Plugins Name : QuadFace Tools
Downland
https://extensions.sketchup.com/exten...
https://extensions.sketchup.com/exten...
import .obj to sketchup
obj importer for sketchup