Click the 
button on the quick access ribbon toolbar
Press CTRL+Z.
To cancel the last operation of data change:
Click the button on the quick access ribbon toolbar
Press CTRL+Z.
If changed data was saved and then the saving operation was canceled, then previous values will be returned. Those values will be highlighted as changed and to further use them, save them.
To redo the last undone operation:
Click the 
button on the quick access ribbon toolbar
Press CTRL+Y.
The / buttons on the quick access toolbar are active on changing data.
On refreshing data entry form and calculating algorithms for saving, the operation history is cleared and the / buttons on the quick access toolbar deactivate.
NOTE. The items are available in the desktop application.
See also:
Working with Ready Data Entry Form