Object > Generative > Generative Expand

Select the Scene you’d like to extend/resize before going to the menu command above, using the Generative pop-up at the bottom of the Toolbar, the button at the bottom of the Properties panel or in the Contextual Task Bar, or click the icon on the right in the Control bar. A prompt is optional, but isn’t required.

Note – whether you used one of the Partner models to generate your scene or not. There doesn’t appear to be a way to use any of these here, so we assume that the Adobe Firefly Vector model is what is being used (incl. 3 variations with each click)