It is easy look at the vertical blind diagrams at http://www.fixmyblinds.com/Instructions-to-Fix-Your-Blinds-s/475.htm - You will have to alter the clamping of the cord and it may be easier to rethread and knot the cord as per the diagram or add a couple of wire circles to clamp the cord. Just follow the relevant diagram. Cheers.
Ron., September 2013