To stream a third-party conference call (e.g. Zoom, Google Meet) to your live stream event, your live stream software should have a setting to enable window capture of the call screen.
You might also need to set the video quality in the third-party web call (normally under Video Settings or Advanced Settings).
Please visit the website of the third-party conference call software and your chosen live stream software to set up window capture accordingly.
Livestream Studio - What is Streaming Software
Livestream Studio - How do I set up my streaming software for my live stream event?