To assign/view student, go to Examination > Exam Group then click on Add icon present at Action column in the exam group list, at the click of this icon Exam List page will be open.
Now click on Assign/View student icon present in the Action column on the exam list page, at the click of this icon Exam Student modal will be open.
Here select the Class and Section and then click on the Search button. Here you can see all assigned or unassigned students for the exam. Now select the student you want to Assign and Unassign for the exam and then click on the Save button.