In your campaign’s Customize section, click on the Poll Choices element to select it.
Now click the Settings tab in the left navigation, and turn on “Show captions”
Next, click the “pencil and paper” icon on the Poll Choice you want to edit. Just under the image, you will now see a blank field titled “Caption”. Enter your caption or description there (be sure to save your changes).
The text you entered will display just below the Poll Choice title: