In the public module you can either edit a session via the menu 'Sessions' or via the calendar via 'Page editor' -> Scientif programme page -> edit the session.
In the 'Session leaders' tab you can press the 'Edit session leaders' button.
Press the green 'Add session leader' button to add your leader.
Choose the type of leader your person is.
Now choose if the person is new, already a session leader of another session or an existing author.
If you choose a session leader that is already in the system and occupied for another session at the same time, you will get a warning.
If you have more than one session leader, you can change the order by clicking on the 3 grey stripes and drag the leader to the correct place.
Removing a leader from this session, can be done with the trash can icon behind the name of the person.