degov-8.x-2.0/modules/degov_social_media_instagram/degov_social_media_instagram.install

<?php

function degov_social_media_instagram_install() {
  $config = \Drupal::service('config.factory')->getEditable('degov_social_media_instagram.settings');
  $config->set('user', "")->save();
  $config->set('number_of_posts', "5")->save();
  $config->set('number_of_characters', "100")->save();
}