For every match you can appoint a referee. For this, in step three of Prepare Tournament click Create referee plan out of participants. Now, there will be as many referees for the matches as there are teams.
If you’re happy with the allocation of referees you can go to Run Tournament and click on Change match sequence, times, fields, placements. Now, you can enter each referee in the column Referee. An appearing yellow frame means that the same referee is supposed to work in two matches simultaneously.
By clicking Save or Save and Return you can save your settings.