When you create a bar line chart, it will default to using the last column as a line. This image demonstrates how Chartio defaults to choosing the last column as a line when you change from a bar chart to a bar line chart.
This doesn’t always make sense given the data you are trying to display. If for example, you want the last 2 columns of data to be lines, you can set this in your Chart Settings under the Series tab.
By changing the “Last X columns as lines” from 1 to 2, now you have two lines in your bar line chart.