The History Brush tool is a great way to
restore parts of an image to an earlier
state.
To use the History Brush tool, first choose
Window > History to open the History
panel. Then, in the History panel, click the
far-left column of the state that you want to
use as the source for the History Brush
tool.
Finally, simply paint over the area that you
want to restore. The History Brush tool is a
great way to fix mistakes or make small
changes to an image without having to start
from scratch.