The first step in seeing Turnitin feedback and your originality report is to Grades in the appropriate course in Canvas.
In the list of grade items, find the assignment that you want to see the originality report for. There should be a small, colored icon to the right of the assignment. Clicking on this icon will bring you to the originality report in Turnitin as well as instructor feedback if the instructor left comments in Turnitin itself.
If there is not a colored icon next to the grade item, that means your instructor has not submitted the assignment to Turnitin and does not yet have feedback.
Note: Instructors can either add feedback using Turnitin or through Canvas' feedback, so check both places for feedback and if you're unsure of which one your instructor uses, please ask your instructor.