Do you mean 3D waterfall? We don't support it direclty in 3D graph. But you can add columns of new XY values based on the offset. Then drag and drop the new Y data into the waterfall.
Usually Z info. from waterfall is read from column header, or long name, comments, etc. You can set it in Plot Details. Layer level. Miscellaneous tab.
Make sure your new Y column has same info. in column label area.