preside at (something)
To exercise authority or control at some meeting, ceremony, or other event. Janet was elected to preside at the board meeting while Tom was absent. They asked me if I wanted to preside at the graduation ceremony, but I declined.
preside at something
to manage or act as chair at a meeting or a ceremony. The mayor presided at the meeting, assuring that the speeches would be very short. She presided at the ceremony.