To access the recovery menu, go to Options from the main screen and click Data Recovery.
A few options will show up if the files required for the recovery are on your machine:
Load Last Run : loads the backup made at the end of your last run (synced with Steam Cloud)
Show Local Backups: shows a (possibly very long) list of backups that are stored exclusively on your machine. Click one of the entries to restore the backup from that version/date/time
Load Old System Data: useful to Mac/Linux users only, this should recover the data saved by the old system that got discontinued since Sunday the 8th of May.
Using this on Windows or for other reasons might yield unexpected results, as the old save system was highly fragmented and prone to data corruption.
