To obtain the information for your scheduled event, you'll want to visit your YouTube Events page and click "Schedule Stream". On the next screen you'll set up your event details.
Once you've created the event, select the event to see the Ingest Server (Stream URL) as well as the Stream Key
You'll then want to import this information into an RTMP Destination by going to "Settings" at the top-right of the screen and then selecting the "RTMP" option listed there in Lightstream Studio!*
*The Premium tier version of Lightstream Studio is required for this option to be selectable.