gb-query-filter.php

<?php 

add_filter( 'generateblocks_query_loop_args', function( $query_args, $attributes ) {
    if ( ! empty( $attributes['className'] ) && strpos( $attributes['className'], 'custom-grid-class' ) !== false ) {
        $query_args['meta_key'] = 'field_name';
        $query_args['orderby'] = 'meta_value'; // better for strings
        // $query_args['orderby'] = 'meta_value_num'; // better for numbers
        $query_args['order'] = 'ASC';
    }

    return $query_args;
}, 10, 2 );

?>