Hello @DONALDH055 ,
Can you elaborate a bit? Are you referring to some of your contacts becoming unsubscribed? The primary way for a contact to become unsubscribed is through the coded SafeUnsubscribe link, legally required at the bottom of every email. Some contacts can become erroneously unsubscribed through an automated action by their ISP, or from someone they forwarded their version of your email to. It's also possible they unsubscribed, rather than updating their profile to reflect what lists they want to be a part of (assuming you have Update Profile enabled).
If you need to resbuscribe a contact, you can do so within the UI. They'll need to make sure they click the link in the resubscription email our system will send them. If for whatever reason they're unable to click that link and confirm the resubscription, you'll want to call into our List Review team to go through the manual override process. This will help ensure there's a paper trail for both legal and Compliance reasons.