Be sure to listen along to the event as it progresses. This means that you will be able to guide the session if you need to and interject at any necessary point.
It also means you will be aware of any technical issues as they arise, so you can respond as best you can. For example, if your speaker loses phone connection you will be able to jump in, avoiding any dead air.
Finally, by listening along you will be better informed for the question and answer session. By this I mean that firstly, you will know who to direct questions to, and secondly you can open with your own statement based on what you may have heard.