Hello @caspe_hannah,
Welcome to the Klaviyo Community!
This would really depend on if you are talking about a list or segment. As mentioned in our Understanding the difference between segments and lists Help Center article, the difference here is that lists are mostly static entities - with some exceptions, whereas segments are dynamic.
Since your screenshot seems to indicate your unengaged email audience is a segment, assuming this is the audience you sent your re-engagement campaign to, users who engaged with your email would typically be removed from the segment automatically - granted that they no longer meet the condition of the segment to consider them as unengaged. If you’re also just getting started, I would suggest taking our Getting Started with Klaviyo Academy Course which goes over some of the basics such as: why deliverability and warming your account is important, how to gain new subscribers with forms, and what is the difference between lists and segments.
I hope this helps!
David