Go to the assignment and click the button to open the Turnitin tool in a new tab.
Click "Upload Submission"
Name your submission and select a submission file from your computer. Once you have done this, click "Upload and Review"
Turnitin will give you a preview of your file. If you wish to "Preview Submission" you can click that button in the bottom left corner. If it is the file you intended to upload click "Submit to Turnitin". Your assignment is NOT submitted until you click this.