The group assignment feature cannot be used with a Turnitin LTI assignment in Canvas. To support group submissions, create an assignment in Canvas and set the submission type as an online submission:

  1. Students submit to Turnitin.com. Marks can be entered directly into Canvas gradebook, imported from Turnitin.com. For ease of access, include in the assignment instructions: assignment ID, password and a direct link to Turnitin.com.
  2. Students submit to Canvas. Bulk-download the students’ submitted works. Upload to Turnitin.com as multiple or zip files to generate originality reports. Provide marks and feedback in Canvas, using Speedgrader.

Note: When the group assignment feature is enabled, you have the option to assign grades to each student individually. By default, Canvas will automatically award the same mark for all the members of the same group.

Read more on Turnitin Guides:
Submitting papers as multiple file uploads
Submitting papers as zip file uploads

Read more on Canvas Community:
How do I create an online assignment?
How do I assign an assignment to a course group?
How do I upload changes to the Gradebook?
How do I download all student submissions for an assignment?