Captions and sub caption of the chart are configured from the 'Caption, Subcaption' panel which is located under the 'General Options' tab.
Caption, Subcaption panel
Chart caption
Use the Dynamic Data button if you would like to use dynamic data for the caption or subcaption of the chart.
Styles can be used to enhance the appearance of the caption and the sub caption. Use the buttons positioned next to the caption and sub caption field to open the ‘Styles Parameter’ panel – from here you would be able to configure the various style parameters.