You have to register for the exams yourselves. This is currently on the (POS).
POS is accessible at: https://noten.hs-mannheim.de
The registration time for the exams is approximately from the 10th week till the end of 14th week after the start of Lectures for a Semester (for exact dates: Homepage → Studierende → Semestertermine). Failing to register in this time frame results in a candidate not appearing for the exam.
Deregistration for an Exam can be done till a day before the exam. That means one has to deregister before 23:59 hours on the day before the exam to be successfully deregistered for an exam.