The Undo command on the Edit menu or toolbar will undo the last change you made to the current section or analysis. CFS keeps track of the last 10 changes made to each open section and analysis, so you can undo multiple changes.
The Redo command on the Edit menu or toolbar is available after you use Undo with the current section or analysis. This will redo the most recent Undo change, and can be used repeatedly back the first Undo made.