Click the Home | Undo | Redo command or press CTRL+Y on the keyboard to reverse the last Undo command.
After you have used the Home | Undo | Undo command, the Redo command indicates the operation that you have undone. Hover the cursor over the Redo command to see the last undone action. For example, after deleting an object and then clicking Undo, the Redo command tooltip displays Redo Deletion.
Click the Grid Editor | Undo | Redo command or press CTRL+Y to reverse the last operation performed when in the grid editor view.