This is the look of the tool GUI.
The left scripts list panel groups the JS actions by type. It contains a tab selector for the document level scripts, the document event JS actions and the page events JS actions. When operating in single file mode, and only if the document has related JS actions, it shows a tab selector for screen annotations and interactive form fields.
To change an already existent script there is only the need to select it, from its type group tab, and use the, at right, text editor to edit it. The top right toolbar scrip name field can be used to change the name of document level scripts.
Each of the tab selectors has a toolbar with buttons to create a new script and to delete the selected one. When the new script button is clicked it opens a settings sub-panel where there are options to define the JS action characteristics, such as the event that will fire it and/or to what document page it will be added.
Even in single file mode, changes are not immediately applied to the document. The bottom left preview button is used to temporally apply the changes and automatically open the default PDF reader, in order to see how the scripts are working. The run button is used to definitively apply the changes, and the cancel button can be used anytime to exit the tool without applying any changes.