Replace 123 with the ID of your form. Replace role="form" with your custom attributes.

add_filter( 'frm_form_attributes', 'add_custom_form_attributes', 10, 2 );
function add_custom_form_attributes( $attributes, $form ){
    if ( $form->id == 123 ) {
        $attributes .= 'role="form"';
    }

    return $attributes;
}

If you would like to stop the tooltip error messages from your browser such as the tooltip shown on custom number range validation messages, use the code below. Replace 123 with the ID of your form.

add_filter( 'frm_form_attributes', 'add_custom_form_attributes', 10, 2 );
function add_custom_form_attributes( $attributes, $form ){
    if ( $form->id == 123 ) {
        $attributes .= 'novalidate="novalidate"';
    }

    return $attributes;
}

If you would like to publish your form on an AMP page, use the code below to add the necessary AMP attributes. Replace 123 with the ID of your form.

add_filter( 'frm_form_attributes', 'add_custom_form_attributes', 10, 2 );
function add_custom_form_attributes( $attributes, $form ){
    if ( $form->id == 123 ) {
        $attributes .= ' action-xhr="https://ampbyexample.com/components/amp-form/submit-form-input-text-xhr" target="_top"';
    }

    return $attributes;
}