If you, as a student, have overlapping exams and want to use the "double exam" facility, you need to make a request to the Examination Office at least two weeks in advance. You can do so by filling out the request form. The Examination Office forwards your request to your study adviser for permission and usually this will be granted. The Examination Office informs you about where and when you are expected to take the double exam.
Please note: If you're requesting extra facilities due to personal circumstances, make sure that you have informed your study adviser about it beforehand.
More information about exams and exam-taking can be found on the website of the Examinations Office.