Turnitin is available as an external tool.
Here's how to add a Turnitin assignment to a course:
1. Go to the course and add a new assignment.
2. Set up the assignment normally
3. Change the Submission Type to External Tool.
4. Under External Tool Options click on Find
5. Scroll down the list until you find Turnitin and click on it then click on Select
6. You will return to the Submission Type. If you want Turnitin to open in a new tab (recommended) check the box Load this tool in new tab.
7. Finish filling out the Assignment
8. Click on Save