For anyone playing the preview version of the game who wants to keep their save data after launch, please follow the following steps:
1) Open the install location of Berserk or Die (right click the game title from the Steam Library, then Manage > Browse local files
2) Copy these files from the "BeaserkorDie_Data" folder
3) Paste them into "BerserkorDie_Data" folder
Now launch the game and your old save data will be loaded. Please just send a message on the forum if you need any help, thank you!