REGULAR STUDENTS have to apply via QIS !
GUESTSTUDENTS should have a look in QIS if you can register for your exams.
If you can: great!
If not... THEN and ONLY WHILE BEING A GUESTSTUDENT you have to REGISTRATE FOR EXAMS in this way:
Fill in the "application for a transcript" with all subjects you want to have recognized and hand this in to the International Office till 15th of January in winter term and 15th of June in summer term. (You can leave blank "course of study".)
And however, all gueststudents who want to get a transcript have to hand in this document at some time.
If you need a confirmation of stay for e.g. Erasmus you should talk to the International Office or your departemental coordinator (the persons who know your exact arrival and departure dates).