|You can't really.|
RAW isn't really a file system, it is what Windows reports when it doesn't recognize the file system. This usually happens when the drive is corrupt or failing. There are utilities available that may allow recovery of at least some of the data.
Flash drives are the least reliable of modern storage media and they should not be trusted for long term storage of important data. If possible you should have this data stored elsewhere, such as the hard drive of a computer.