Hello Ejaz, Go to the "Class name". Look for "More actions" to the extreme right under your "assignment". Go to "Edit Setting", then "Optional Settings". Go to "Submit papers to:" and select "no repository"
I believe the manuscript will never be saved to the database.
However, if it detects plagiarism from archived documents, it will indicate such in the result and it will be easy to identify that the document had been submitted earlier