Go to Webinar > Upcoming from the left navigation bar in your RingCentral app.
Click the Start button beside your scheduled webinar.
The Start Webinar popup window will appear. Click Start if you are sure to start the webinar.
Clicking start will start a prep session with your co-hosts and panelists. Attendees will be waiting in the lobby. Click Go Live on the bottom right corner when everything is ready. Once you go live, the attendees will then join the webinar.