Maybe you can set two columns as Y error, one is plus error, another is minus error.
The steps are below: 1.First set the columns with proper plotting designations such as X, Y, X error and Y error, please note that you should have two Y error columns. 2.Select the data you want and click the desired plot type on the 2D Graphing toolbar. 3.Double click the graph to bring up "Plot Setup" dialog box. Select an error bars icon beneath the associated data plot icon on the left side of the dialog box, in the right panel, you can set the direction of them as "Plus" or "Minus". Please see for here detailed information on this dialog.