You cannot write data's to asset/Raw folder, since it is packed(.apk), the assets folder is read-only at runtime.
You need to choose a different storage location, here is a method to backup you db to your sdcard (external storage) dbName=MyDataBase.db in your case:
public static void backupDBonSDcard(Context context, String dbName){
    String DB_PATH = context.getDatabasePath(dbName).getPath();
    Log.d("DB_PATH:" + DB_PATH);
    if(checkDataBase(DB_PATH)){
        InputStream myInput;
        try {
            Log.e("[backupDBonSDcard] saving file to SDCARD");
            myInput = new FileInputStream(DB_PATH);
            // Path to the just created empty db
            String outFileName = Environment.getExternalStorageDirectory().getAbsolutePath() + java.io.File.separator + dbName;
            //Open the empty db as the output stream
            OutputStream myOutput;
            try {
                myOutput = new FileOutputStream(outFileName);
                //transfer bytes from the inputfile to the outputfile
                byte[] buffer = new byte[1024];
                int length;
                while ((length = myInput.read(buffer))>0){
                    myOutput.write(buffer, 0, length);
                }
            } catch (FileNotFoundException | IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } finally {
                //Close the streams
                if(myOutput!=null){
                    myOutput.flush();
                    myOutput.close();
                }
                if(myInput!=null)
                    myInput.close();
            }
        } catch (FileNotFoundException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
    }else{
        Log.d("DB "+dbName+" not found");
    }
}
public static boolean checkDataBase(String fileName) {
    java.io.File dbFile = new java.io.File(fileName);
    return dbFile.exists();
}
Don't forget to add the following permission in your manifest:
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />