I have found the solution from here. And its working!

WordPress has a set of restricted filetypes it will allow you to upload via the media library. Whilst this is a great security feature, there may be times where you’d like to add other files that are restricted by default, or maybe even the opposite where you’d only like to allow a few extensions to be uploaded. Fortunately, WordPress makes this dead easy with a small snippet of PHP code.

If you’d like to add or remove a specific filetype that can be uploaded to wordpress via the media library, you can insert this PHP code in your theme functions.php file:

function my_myme_types($mime_types){
//Adjust the $mime_types, which is an associative array
//where the key is extension and value is mime type.
    return $mime_types;
}
add_filter(\'upload_mimes\', \'my_myme_types\', 1, 1);

Here is an example of what you can do to add and remove a new filetype (in this example, I’m adding an extension that already exists, but the concept is the same):

function my_myme_types($mime_types){
    $mime_types[\'avi\'] = \'video/avi\'; //Adding avi extension
    unset($mime_types[\'pdf\']); //Removing the pdf extension
    return $mime_types;
}
add_filter(\'upload_mimes\', \'my_myme_types\', 1, 1);

You can also reset the allowed filetypes by creating a new array within the function and returning these values:

function my_myme_types($mime_types){
    //Creating a new array will reset the allowed filetypes
    $mime_types = array(
        \'jpg|jpeg|jpe\' => \'image/jpeg\',
        \'gif\' => \'image/gif\',
        \'png\' => \'image/png\',
        \'bmp\' => \'image/bmp\',
        \'tif|tiff\' => \'image/tiff\'
    );
    return $mime_types;
}
add_filter(\'upload_mimes\', \'my_myme_types\', 1, 1);

If you’d like to see what filetypes are currently supported by wordpress, check out the function get_allowed_mime_types located in the wp-includes/functions.php file.