How to set the form field after validation

How to set the form field after validation? Before validation it’s posible:

add_action('wpcf7_posted_data', 'my_fun', 10, 1);

function my_fun($form_data) {
  $form_data['my-field'] = 'some value';
  return $form_data;
}

But how can I achieve this after validation?

add_action('wpcf7_before_send_mail', 'my_fun', 10, 3);

function my_fun($cf7, $abort, $submission) {
  // ??? = 'some value';
  return $cf7;
}

add_action('wpcf7_submit', 'my_fun', 10, 3);

function my_fun($cf7, $result) {
  // ??? = 'some value';
}

I have hidden input in my form. My goal is to set this field with data from external API (but after form validation).