Ideally, you want to enter the video ID/URLs for your live or pre-recorded talks before they are meant to go live (ongoing).
If a talk goes live before it has anything set up in its Video Settings, you would get the Replay Details option automatically, as you can't modify the video Settings for a talk that is live.
Once a talk goes live once, it can't be live again- it will remain a replay.
If you would like to add more content to your summit as it goes on, you must add a whole new talk.
Do make sure you create the talk and add the video ID/URL quite a bit before the talk is slated to go live.
- To add a new talk, go to Content > Talks.
- Click on + Add Talk
- Fill in the information for the talk