Each time you open a file, the Heredis software creates a copy in .bak format. This copy contains all the information previously entered, but it does not contain the information you have added since the last time you opened the file.
Restoring this copy will allow you to recover all the data entered before the last opening.
Here is how to proceed to restore from .bak safely:
Open the software on its homepage and click on the cogwheel to the right of the name of the genealogy concerned: