You can access the configuration settings of the Two Dimensional Widget by clicking on the blue arrow at the right side of the widget.
The Two dimensional widget saves your configured settings permanently. Your configuration persists even if you change items or groupings on the board. You can change the settings of your widget at any time. This widget type can't get viewed or configured by users of the type viewer. You can read more about user types in the official documentation by monday.com.
After successfully configuring the widget, an info text gets shown below the table, detailing which numerical column gets summed up by which categorical columns on the x- and y-axis.