How to move contacts between lists
If you'd like to move your subscribers from List A to List B, you'd have to do that manually. First, export your subscribers from List A.
Then,
re-import them into List B.
Since our lists are treated independently, the contacts you've just exported will still continue to exist in List A and count towards your contact limit.
To bulk unsubscribe from List A, go to "Add contacts", click on "Import contacts from a file", and then select Unsubscribed and Update existing contacts. Finally, click and select the list of contacts that you've just uploaded to List B and click on Next.