There are two ways to back up your ZenLedger data to ensure that you have access to previous work that you've done on your account.
ZenLedger Backup (Snapshots)
With the Snapshots feature, you can quickly back up your work anytime on ZenLedger's servers to make sure you can revert to an earlier time if you make any mistakes. See this article for more detail on Snapshots.
Personal Backup (CSV)
See this video for a walkthrough for the steps to download all, or part, of your ZenLedger data to your computer.