Ok. Did you uninstall the add-on 1st....
1st go to system, add-ons, install from repository now go to Operation Robocop and go in. Now go to video add-ons and hover over Robocop and press the menu button, in that menu that pops up go to add-on info, now you can uninstall it.
Now go back to the repo and do the same, as you need to uninstall that too.
Now go and try the the link again.
https://seo-michael.co.uk/tutorial-how-to-install-operation-robocop-video-add-on-kodi/
If I remember the version of robocop should be 2.0 now, hope this helps you..