Edit the functions.php file of your WordPress theme:

.../wp-content/themes/mytheme/functions.php

Add the following text to allow for a specific file type:

function my_myme_types($mime_types){
        $mime_types['blend'] = 'application/blender';
        return $mime_types;
}
add_filter('upload_mimes', 'my_myme_types', 1, 1);