To Undo all Operations Recorded in the Undo Buffer
Do one of the following:
On the Quick Access ToolBar, select All from the Undo drop-down list.
or
In the Key-in window, key in UNDO ALL or UNDO ALL NOCONFIRM.
or
If the preference Automatically Save Design Changes is off, close the open DGN file without saving changes.
This preference is set in the Operation section of the Preferences dialog ( ).