Once you have published your Webstory, it is saved as a backup that you can restore.
To restore the previously published version, open the web story you want in the builder. Then, click on SET UP, in the top left corner of the interface.
When the settings appear, click on " Versions " (the last section of the menu).
You will see the latest version that you can restore with the date and time (Published version).
The other one is the actual version you can see & modify on the editor (Draft version).
If you want to restore the latest published version, just click on REROLL DRAFT TO PUBLISH.