Attendance officers need a way to update exams attendance - particularly if students are out of lessons for an exam that happens first thing in the morning/after lunch.
On lesson dashboards, teachers are notified if any of their students are in an exam. You can see how this works here: How can teachers tell if a student is due to be out of the lesson?
You can update attendance marks for students who have had an exam by using one of the Bulk Edit Marks pages: Bulk editing attendance marks
Just select the exam in the filters.
It's likely these students will have been marked absent from their lesson because they were not with the teacher, but instead in the exam. You can then change their mark to say they were in school, in the exam.