To convert the existing bar chart into a stacked bar chart, the associate should drag another dimension to Color on the Marks card. The initial bar chart already contains a dimension on Columns and a measure on Rows. Adding another categorical dimension to Color partitions each bar according to the members of that second dimension. Tableau assigns a separate color to each resulting group and, because automatic stacking is enabled for bar marks by default, those groups are displayed cumulatively within each bar. For example, if Category is on Columns and SUM(Sales) is on Rows, adding Segment to Color divides each Category bar into Consumer, Corporate, and Home Office segments while preserving the bar's total Sales magnitude. Dragging another dimension to Size changes the visual size encoding rather than creating standard stacked segments. Adding another measure to Rows typically introduces an additional axis or measure structure. A measure placed on Color generally creates a quantitative gradient rather than categorical stacked segments. Tableau's official Stack Marks documentation describes this exact construction: a dimension on Columns, a measure on Rows, and another dimension used to color-encode the marks.