You don't have to install the grader again. It's already installed from before. When you try to install it when it's already installed you get that error message. Just use the grader app by clicking the App Launcher and selecting the grader.
You don't have to install the grader again. It's already installed from before. When you try to install it when it's already installed you get that error message. Just use the grader app by clicking the App Launcher and selecting the grader.