In the program, create a smart list with the filter "Member of program - Program Name" with the constraint "Progression status is Registered". Your flow is Send email. Schedule this campaign to go out 24 hours prior.
In the future, you can set up a reminder campaign and use wait steps to determine when to send the reminder email. There is a good example of a webinar built out in the Program Library. You might want to connect to it and import this program into your subscription for the future.
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