You should be using the Clone Stamp Tool non-destructively on it's own layer. If so, then just use the Erasure Tool to remove the unwanted content.
However, if you are working destructively on the image itself, about the only thing you can do, besides undoing steps, is to again replace the stars you want to remove with some other means such as, Clone Stamp, Content Aware Fill, Content Aware Move, Patch, Healing Brush, Spot Healing Brush Tools.
Without seeing the work, it's only a guess on my part though. Hope this helps.
Another option to consider is to either back up in the history with Undo or use the history brush. How far you can go back depends on the number of history states you have allowed to be saved in Preferences in the Performance section. Here is a link that covers the details: https://helpx.adobe.com/photoshop/using/undo-history.html