The action is still Modify Variable.
But, under your value, you will see a drop-down box that allows you to either Set Variable or Add to Variable. Unless you're doing some sort of quiz or possibly some simulation, you likely don't need to Add to Variable. And, usually, you don't need to add strings (though I will if I am changing the contents of a text box). In this case, adding strings might not be a bad deal for you.
Kevin
