You can undo an action:

The command Undo can resolve errors during input or editing, when you select it directly after the last change. For example, if you delete a component or signal by mistake, it is possible to Undo this last step and reload this component or signal again. This command can be selected by clicking on the tool or through the Undo command in the File menu. TARGET 3001! can undo 50 steps. For tidying up the internal database a "Reorganisation" in Menu "Actions" from time to time is recommended.