You would add a "Wait" step to your Campaign Flow.
So your Trigger would be something like "Data Value Changes", where the value is "Launch is TRUE" (or whatever you've set up in your CRM).
Then your Flow would be "Wait: 7 Days", "Send Email" (or "Add to Engagement Program", which it sounds like you have set up).
However, if you want to make sure the email fires immediately on the seventh day (without worrying about your Engagement Program cadence), then I would use the Send Email flow, THEN add them to the engagement program.
I hope this makes sense!