On my mp4 i try to delete a file and it says cannot read source file corrupted and unreadable what do i do?

everytime i plug in my mp4 it loads it and ill try to delete a file that i previously put on but it now says cnnot read source file the file is coruppted and and unreadable i go in to try to override it but its all written in like korean or something if u know how to delete the mp4 completely to put it back to the way it was as if u just bought it please let me know how or if u have a link for the firmware upgrade please let me know that too thanks