Select at least two columns of values or a range of values from at least two columns. Plot designation does not matter; selected columns will be treated as Y columns.
For information on the customizing allivial diagrams, see these topics:
Sankey.otpu (installed to the EXE folder of Origin)
Sankey diagram is another kind of alluvial diagram, which also has rectangles for "nodes", colored areas(linking "nodes") for "links", vertical groups of nodes for "steps".
The difference is that the source data of Sankey diagram are raw data, the node values of which haven't been arranged as multiple columns for the steps.