You can change the configuration of a site under Data Collection Portal > Site Management > Edit site and if needed make sure to also add extra domains as complementary URL of the site.
This URL is important in order to correctly define the source of the visit, when it starts from your website.
This will allow to ensure that all domains tagged using this level 1 site will be taken into account as a part of the website (to ensure the measurement of direct access (continuation of visit), use the Portal option, make cross-domain analyses ...).
This change is taken into account at midnight, the next day.