Hi @katherine_byers Welcome to the Canvas Community. This is a good question and has come up in the past mainly when dealing with the LTI version of Turnitin, specifically, which functions as an external tool. Full credit to the folks who contributed to this similar question, which also has a link to a feature idea: How to Add a Canvas Rubric after TurnItIn LTI submissions received? I realize that in your case you already have a rubric but just want to get to that checkbox enabled, but I believe the workaround mentioned in the answer should still work: basically, change the submission type to online rather than external tool so that you can get access to that rubric options again, and then turn it back again once you enabled it. While I know from personal experience when testing out the Turnitin LTI that it will work, you might want to try it out on a test assignment first, perhaps even submitting something while in Student View, since it may also depend on whether you have already received submissions or not. Again, this is not an issue with Turnitin, but it may be with whatever tool you are using. (I just believe in playing it safe to be sure!)
I hope this helps a bit, Katherine.
Hi @katherine_byers ...
I realize this is an older question in the Community, but I just reviewed part of the June 21, 2023 Deploy Notes, and there's a section on Assignments: External Tools Add Rubric Button that I think you'd be interested in reading more about. Here's a link for you: