Managing attendance can be done on the Students screen.
Next to each student's name, there will be an orange clock at the far right. This will take you to a new screen, like below:
Here, you can add or remove sign in and sign out records, add or remove absent records, and modify activity records, all for past or future dates.
You can add sign in and sign out records by tapping the gray "Time in" or "Time out" boxes. To remove sign in and sign out records, you can tap the gray "X" to the right.
Absent records can be added by tapping the yellow Absent button at the top right.
Attendance records can be modified by tapping any times that have already been inserted and changing them.
Records can be moved to past or future dates by tapping the arrows at the top left and right corners.