Click the 
Undo Action button on the quick access toolbar of the ribbon.
Press CTRL+Z.
To undo the last operation in a data entry form:
Click the Undo Action button on the quick access toolbar of the ribbon.
Press CTRL+Z.
If changed data was saved and then the saving operation was undone, previous values will be restored. Those values will be highlighted as changed and to further use them, save them.
To redo the last undone operation:
Click the 
Redo Action button on the quick access toolbar of the ribbon.
Press CTRL+Y.
The Undo Action and the Redo Action buttons are enabled on the quick access toolbar if the data was changed.
When refreshing data entry form and calculating algorithms for saving, the operation history is cleared and the Undo Action and Redo Action buttons are disabled on the quick access toolbar.
See also:
Getting Started with the Interactive Data Entry Forms Extension in the Desktop Application | Working with Ready Data Entry Form