I have no experience with the widget itself, but the screenshots show an attribute that stores the search string during execution of the search microflow. In the microflow you can use the value of the search string in any way you'd like. So if you use Xpath as source, you could try to switch to microflow.
If you use it as a text box, it must be in a dataview however. This dataview should probably contain an object of the entity you selected for the widget, including the attribute that you selected in the widget settings. If you press save, it should be handled as a regular textbox and simply save the value to that attribute. You can easily check this by replacing the save button with a microflow button that does the same. Debug it and check what value the attribute has.