The undo brush can be found in the tools panel. If it is not then you will have to get it via the view menu and customise tools.
You need to set a history state or source for the tool via the history panel and that can be done by going to the panel and clicking on the left side of any entry in the history panel and the tool will then use that 'image' as the source, though it is the underlying image and not any image modified by live layers etc
You can use it with shapes, images, type, etc