When creating or editing a contact under Settings (gearwheel) > Press contacts, ticking the checkbox that says Pin press contact, will make the press contact appear on the front page of your newsroom (in addition to the listing under the Contacts tab). Moreover, the publications that you create will by default automatically include your pinned press contact(s) as Related press contacts, unless you pick different press contact(s) manually for the occasion.

If you at some point change the setting and pin other press contacts, these will update accordingly both on the newsroom front page, and as Related press contacts in your publications. This is also the case for publications that have already been published, unless the Related press contacts were manually changed when editing a material – in that case the individually set Related press contacts will keep showing, regardless of which press contacts are currently pinned.

Please also see:
Where do I add or edit a contact on my public newsroom?
Can I change a material after it has been published?
Publish a press release, news or blog post