How do I add new curves to a plot?

1. Open the saved plot.
2. Either open a new data set or choose Extract Data from the Plot menu to display the original data used to create the plot.
3. Switch from the data window to the plot that was opened.
4. Choose Template from the Gallery menu.
5. Select the variables you want to plot and click New Plot. A new plot will be created using the saved plot as a Template.