Hi Christina,
Quick question. Why not just add the content to Stream 1? After all, they won't get it until they've exhausted the content above it anyway.
If there is a reason why you want to do it in another stream, you could create a Smart Campaign that runs nightly or weekly (depending on your cadence) to move them. The filter would be as pictured. The flow would be "Change Engagement Program Stream".
Best,
Mike