In Canvas, if your instructor has turned on the TurnItIn setting, you just need to submit the paper to the dropbox, just as you would normally do for grading. The paper will automatically be run through TurnItIn, which is embedded in Canvas.
Resubmitting Assignments: Permitted in Advance
If your instructor has set up the assignment to permit you to resubmit an assignment, you will be able to do so until the due date. Follow the instructions for the initial submission to resubmit the assignment. You can only resubmit three times to receive an immediate similarity report. After that, you will have to wait 24 hours to receive the similarity report.
Resubmitting Assignments: Not Permitted in Advance
If your instructor has not set up the assignment to permit resubmission, then you will have to contact the instructor and they will have to manually delete the previous submission before you can resubmit the assignment.