To log in to a specific Turnitin class for your "piece" (assignment), you need Enrollment Key (password) provided directly by your instructor or institution
Troubleshooting Tips
How can I find the class ID and class enrollment key ... - Turnitin turnitin login class id and password
To join a class on Turnitin, you need two specific pieces of information provided by your teacher or professor: To log in to a specific Turnitin class