You can undo a edit or return to the last edit points.
"Undo" button in the edit bar
Click Undo once, you can undo the last edit in the timeline. By continually clicking "Undo, you can return to a few steps back. The keyboard shortcut for Undo is Ctrl+Z.
"Return" button in the edit bar
"Return" is to return back to the last edit after you click "undo". It will return to the edit point before you click "undo". The keyboard shortcut for "return" is Ctrl+Shift+Z.
Tip: The "Return" button is only activated after you have clicked the "undo" button.