Rubrics + External Tools

Currently, I have multiple courses linked to External Tools wherein the grades from the tools are automatically updated in my Canvas Gradebook. Within Canvas, I have assignments created with the external link embedded to take students directly to the proper assignment. (TestOut and MindTap specifically)
I can set a possible amount of points, even if it doesn't align with the pre-programmed assignment, but I can not find a place to add a rubric. I would like students to get immediate feedback if they are required to re-take an assessment.

Photos included.