Studying part-time is only possible in a regular semester where the admissions is not restricted and on reasonable important grounds.
You can receive the form to apply for part-time study at the Study Service Center (Studien-Service Center).
For the first application to part-time studies you have to visit the drop-in session with the Student Counselling and Advisory Service.
In case of a repeat or follow-up application you have to prove that you have made a reasonable study progress.
You may receive such a letter of confirmation from the Head of the Examination Office.