Hi,
The quick multi-image functionality is a shortcut and is only available on the initial creation of the slider.
Subsequent edits are done slide-by-slide and you’ll need to add or edit the additional images/slides individually.
We’ve made the plugin use the familiar WordPress editing functionality for the management to make it simpler to use. The add/edit slide screens are identical with the add/edit post or page screens, where the title field will be used as the slide caption title, the text is used as the caption text and the featured image becomes the slide (image) itself.
Sliders behave like post categories, where a slider can (and usually does) hold and display multiple slides (the equivalent of posts).