How to add missing teachers/classes/classrooms in mobile app
At first select a day in daily timetable ("today" is selected by default). Slide the calendar to sides for "previous-next weeks.
Add new absent teacher with big red "+" button in lower right corner.
You can also add more absent teachers (classes, classrooms) in one step.
List of missing teachers will be displayed in substitution with count of their lessons, which have to be substituted.