Turnitin is not just for spotting plagiarism once an assignment is uploaded. It can be used to teach students about plagiarism.
You can allow students to upload a version of an assignment and generate a similarity report as many times as they like before the due date.
This will give you a chance to go through the report with them to identify errors in citations or referencing, and to understand what the report is actually saying.
Watch the video to see how to allow multiple uploads in Turnitin.