Change tooltip on hover

[David]

I see a lot of example, but nothing works for my simple example. I am trying something like that

 function OnSeriesHover_EconomyRelationshipsLevel2(sender,args) {
               if (args.category == "30") {
                  args.series.tooltip.format  = "Click for Details";

                  sender.series.tooltip.format = "Click for Details";
               }
            }

Thank you