Select the Discussions tool from the tool menu of your site.
Note: You must have an existing Gradebook item in order to associate the forum topic with that item, and the gradebook item must already have the rubric attached. If there are no existing items, you will need to go to the Gradebook to create the item first.
Once you have selected a gradebook item with a rubric, you may select Preview Rubric to see what the selected rubric looks like.
Note: If you want to select a different rubric, you will need to go to the Gradebook and modify the gradebook item to use the new rubric. If you need to make changes to the rubric itself, you will need to go to the Rubrics tool and modify the rubric criteria and ratings.