I don't think we have such undo mechanism Out-Of-The-Box. It could be quite complex to undo anything with Pega. Just a change on a field could trigger other actions on different WorkObjects all over the place.
I guess you will have to create a custom one based on your specific requirements.
hi, easy solution would be to take a snapshot of your current section and store them in clipboard (as list) every time a change is made. When "undo" button is clicked you could pop the last one from that page and refresh the section.
I am not sure what Pega version you are on but 8.1 has a runtime authoring capability with undo/redo last 10 changes. So let me know what version you are on and can point out a working example.