How do I edit the subject line for each email in a drip series?

I created a 14 day drip campaign for our users who signed up for a 14 day trial. 

I can't seem to find how to edit the subject line for each of the emails. The subject lines are all blank.  I know when I create a single email I have a settings section where I can write the subject and he preview text. 

I can't seem to find that option for a sequence of emails.