In Sleek Bill Online there is no need to backup your files.

The benefit of using Sleek Bill Online is your files are safe and they will still be there when/if you have any problems with your computer. You can just login after your reinstall your system, or login from any other computer or tablet, and you will see that your data is still here.

Do you want to backup your files in Sleek Bill for desktop?
In the desktop version, please go to Tools -> Backup Data, click on Backup and then Save your file.
For details please see: http://prnt.sc/f3ncdc