How do I retrieve a previous version of a character?

I accadentaly deleted my character's backstory and I want to retrieve it

There's no versioning on the character sheets. IIRC, people have been able to recover accidental full deletions by contacting support, but I don't know if they'll be able to help you with a smaller change.

It can't hurt to ask. They're often slow to respond, though. 

If they can help you, it'll probably be by restoring the character as a whole to a previous version, so copy the character as it is now and play with the copy.

I can no longer access any of my characters