Study the research profiles of the professors in your department (links: see here, under Philologies; only those with a Prof. Dr. title are eligibile as supervisors). If you think that your dissertation project might be of interest, write to the relevant person with a project outline and your CV. If you are able to secure a supervisor, then enroll as a doctoral student and subsequently apply to the Doctoral Program in Literary Studies. For more information, see the Guidelines Doctorate.

If you are not successful, then your project is not mature enough, does not coincide with the research interests of the supervisors in question, or they do not have the capacity to supervise other doctoral students.