If your school-leaving qualification is not considered equivalent to the German Abitur, you may be able to attend a Studienkolleg (preparatory college) in Germany and subsequently take the Feststellungsprüfung (University Qualification Assessment Examination), which is recognised as a higher education entrance qualification.
Unfortunately, the University of Siegen does not have its own Studienkolleg. Please consult the website of the Studienkolleg in Germany for further information.
Prospective students who have successfully passed the Feststellungsprüfung must apply to the Starting department within the relevant application deadlines.