piklist-filter-piklist_pre_update_option_$setting

<?php 
  //When the user enters data in the piklist_demo_fields settings page and they press save, add another setting called option_key with the value of option_value.

  add_filter('piklist_pre_update_option_piklist_demo_fields','my_update_option',10,4);
  function my_update_option($settings, $setting, $new, $old) {
   
      $settings['option_key'] = 'option_value';
   
    return $settings;
   
  }