It is not possible for students to self-check a paper within Turnitin without submitting it to an assignment created by an instructor unless your institution has enabled Turnitin Draft Coach* for your institution's Turnitin account.
If an assignment allows resubmissions, you may be able to resubmit a paper several times before the assignment’s due date, and any second or subsequent submission will overwrite the original submission in this assignment. You are allowed three resubmission attempts where the Similarity Report will be generated immediately; after three attempts, you will have to wait 24 hours before a new Similarity Report can be generated.
If resubmissions are not allowed, your first attempt will be final. If you wish to check a paper beforehand, you will need to ask your instructor and see if they are willing to set up a separate assignment for this specific purpose.
*Note: Please check with your institution if access to Turnitin Draft Coach is available to you - this allows students to effortlessly run a Similarity Report and check a document for similarities against our vast database, which also includes citation and grammar checks.