It's super easy to turn your bar chart into a stacked version.
To begin, click Tools, then click Charts in the left panel in the Piktochart editor.
Next, the chart window will appear, and you can then find chart settings in the right top corner.
Only for the horizontal or vertical bar chart you can create a stacked bar chart. This will not be available on any other charts but those two.
To make the bar charts stacked, use the slider to turn On or Off the Stacked toggle. Here is a quick image of where to find this option.