def mark_unread(self, **kwargs):
response = self._requester.request(<EOL>'<STR_LIT>',<EOL>'<STR_LIT>'.format(<EOL>self.course_id,<EOL>self.assignment_id,<EOL>self.user_id<EOL>)<EOL>)<EOL>return response.status_code == <NUM_LIT><EOL>
Mark submission as unread. No request fields are necessary.

:calls: `DELETE
    /api/v1/courses/:course_id/assignments/:assignment_id/submissions/:user_id/read \
    <https://canvas.instructure.com/doc/api/submissions.html#method.submissions_api.mark_submission_unread>`_

:returns: True if successfully marked as unread.
:rtype: bool