How to find attachment by it’s name?

You have to write custom code to get the attachment id and post_parent by name/ slug or filename(if it has not been changed during the uploading of files).

Put the below code in your theme’s functions.php file

if( ! ( function_exists( 'wp_get_attachment_by_post_name' ) ) ) {
    function wp_get_attachment_by_post_name( $post_name ) {
            $args           = array(
                'posts_per_page' => 1,
                'post_type'      => 'attachment',
                'name'           => trim( $post_name ),
            );

            $get_attachment = new WP_Query( $args );

            if ( ! $get_attachment || ! isset( $get_attachment->posts, $get_attachment->posts[0] ) ) {
                return false;
            }

            return $get_attachment->posts[0];
    }
}

then you can call the function where you need it like below :–

$attachment = wp_get_attachment_by_post_name( $post_name );
// Replace post_name by the name/slug of the attachment
// It will give you an object, which you can render like below to get the ID and post_parent
if ( $attachment ) {
    echo $attachment->ID; // Gives the id of the attachment
    echo $attachment->post_parent; // Gives the post_parent id
    echo $attachment->post_title; // Gives the attachment title.
}