Make a backup of your site and go to your functions.php file using an FTP client:

1. Access your WordPress installation directory (in most cases, it’s public_html) via an FTP client or File Manager.

2. Navigate to wp-content -> themes -> current theme’s folder

3. Open the functions.php file

4. Type:

function my_custom_mime_types( $mimes ) {

// Add new MIME types here

$mimes['abiword'] = 'application/x-abiword';

return $mimes;

}

add_filter( 'upload_mimes', 'my_custom_mime_types' );

5. As always SAFE your changes

By adding the upload_mimes filter to functions.php, the behaviors of your WordPress site will change. It will be no problem to upload a before prohibited file type.

Use the upload_mimes WordPress filter hook

Open the functions.php file of your WordPress theme.

At the top of the file type this code:

// Add this to the functions.php file of your WordPress theme
// It filters the mime types using the upload_mimes filter hook
// Add as many keys/values to the $mimes Array as needed

function my_custom_upload_mimes($mimes = array()) {

// Add a key and value for the CSV file type
$mimes['csv'] = "text/csv";

return $mimes;
}

add_action('upload_mimes', 'my_custom_upload_mimes');

$mimes['csv'] = "text/csv" is for a file with csv as extension. The mime type for csv is text/csv. 

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