Answer
First, check whether you actually need to unpublish the page at all to change the Datasource Entity Set — it may be possible to set it directly without unpublishing first, which sidesteps the missing-three-dots problem entirely. If the menu still isn't showing after that, clear the Aurena projection, metadata, and lobby caches and restart the client — a stale cache is the other common cause of Page Configuration UI elements like this three-dot menu failing to render as expected.