Hey @Laura40! If those subscribers have already been marked as completed on the sequence, we'll have to re-activate them for you before they'll receive any additional emails from it. Feel free to reach out to our team at firstname.lastname@example.org (or via the in-app messenger in your account) with the sequence you want the subscribers re-activated on, and one of our Product Specialists will help you out with that!
We also have this article that you might find useful: Will My Existing Subscribers Receive New Emails Added to My Sequence?61
I hope that helps! :)