How to send a second campaign to those who didn't open your initial email (unopens)
If you wish to send a second campaign to the group of subscribers who didn't open your initial email send, you will have to do that manually.
Go to the Reports, find your initial campaign and select "View didn't open" in the Activity dropdown, and finally export that list of contacts.
Import those contacts into a new list.
Create another campaign and send it to your newly added list of contacts.