how to manually cancel an unsubscribe


I would like to know if there is a way to "re-subscribe" (ie: cancel an unsubscribe) a member to the newsletters ?

I saw a mysql table named wp_enewsletter_members in which a fiel named unsubscribe_code seams to be empty for all unsubscribed members. Does it mean I just have to insert a random unsubscribe_code again ?