Each time you open a file, the Heredis software creates a copy in .bak format. This copy contains all the information you have previously entered, but does not contain any information you have added since the file was last opened.
Restoring this copy will enable you to recover all the data you entered before the last time you opened the file.
Here's how to restore from .bak safely:
Open the software on its home page and click on the cogwheel to the right of the genealogy name: