How to make the program first check whether a certain classroom is free, and assign lesson to this classroom. If it is busy, then program should select other classroom from the list of other possible classrooms.

The program does not give priority to classrooms when assigns them to the lessons during generation of timetable and picks one from the list of possible classrooms for each lesson.

You can do these steps: after timetable is created, choose “Specification, Change”, Subject – for example, Chemistry, “Change Classrooms, Replace” – Choose Chemistry lab.

Then this classroom will be assigned to chemistry lessons, but some chemistry lessons (if at least two chemistry lessons are at the same time) will remain without the classroom (in the timetable cards of these lessons will be marked with a white stripe on the right edge).

Then choose “Specification, Change”, Subject – Chemistry, “Change Classrooms, Add” and select one or several other possible classrooms.

Then select “Timetable, Assign Classrooms” – the program will assign these classrooms for the remaining chemistry lessons.

Alternatively, if there are not many classrooms that must be fully occupied, you may change classrooms manually in Classrooms preview:

In picture above we moved lesson from Physics lab to Chemistry lab.