The Set Variable action is used to set the values of the selected variables. To configure the Set Variable properties, select the action and click the "Settings" button under the set variable action, the properties windows will be displayed on the right of the workflow designer.
Then click the "Settings" button to open the pop-up window.
Click the "Add" button to add a new row. Select the variable from the left dropdown list, then set the value from the right textbox, or click the "Expression Editor" to add values from the context info.
Click "OK" to save your settings.