EPM reports - how to assign a grid row to a bar and another grid row to a line in combination chart?

I'm migrating reports from report studio to reports but cant seem to find the option in the new reports to allocate a grid row to a bar and another row to a line. I have a grid with 2 rows, one with revenue (to show as a bar) and another with net revenue (to show as a line) on a combination chart but I cant see how to set these parameters - even setting one grid row to dataset1 and the other to dataset2. How do I do this? thanks!