Good evening, @briansoong ...
I believe you are seeing this message because your instructor has not yet fully set up the assignment in your course to utilize the Turnitin interface. There is something that your instructor has to do on his/her end to take care of this...nothing on your end that you need to do. Hopefully by now, your instructor has taken care of this, but if not, I would highly recommend that you reach out to your instructor to let him/her know that you cannot access the Turnitin interface so that you can submit your assignment. You can contact your instructor by following the steps in this Guide: How do I get help with Canvas as a student? - Canvas Community.
I am going to tag @dhulsey in my response just in case he has anything else to add about Turnitin.
Good luck to you! Take care, and be well.