There are two places you can update your subject line.
Edit Subject Line in the Drag & Drop Editor
1. Click Edit under any Draft campaign from the Campaigns tab.
2. Edit the subject line at the top:
Edit Subject Line on Campaign Settings Page
1. Click Edit under any Draft campaign from the Campaigns tab.
2. Click the turquoise Next Step button in the Drag & Drop Editor.
3. Click Next StepĀ on the List Settings page.
4. Update your Subject Line on the Campaign Settings page: