functions.php

<?php

/**
 * Include Form Fields on Confirmation URL
 *
 */
function ea_wpforms_include_form_fields_on_confirmation( $url, $form_id, $fields ) {
    $args = array();
    foreach( $fields as $field ) {
        if( !empty( $field['value'] ) )
            $args['field_' . $field['id']] = $field['value'];
    }

    return esc_url_raw( add_query_arg( $args, $url ) );
}
add_filter( 'wpforms_process_redirect_url', 'ea_wpforms_include_form_fields_on_confirmation', 10, 3 );