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If you're referring to registering your games on the forum, the short answer is you can't, the forum has console sub-forums but otherwise the forum backend complete disavows the existence of consoles.

For a longer answer see:
I assume you're referring to the text found on the "What is Owned Items?" link from the "owned items" sub-page/tab of your profile.
The "code" mentioned isn't relevant for console users. That help and support page does't even acknowledge the existence of consoles. Here's a previous post I made about this (link to that topic/thread):

I'll also note it sucks and is very unprofessional that neither this forum nor support.paradoxplaza.com even acknowledge the existence of consoles with respect to the "owned items" feature of this forum. (I searched the forum extensively a week or so ago about this and found nothing).

E.g. if you go to the "owned items" link for your profile there is a "What is Owned Items?" link that only mentions Steam and then as a footnote says: "If you buy a non-Steam game (GoG, physical disc etc) you will be provided with a code". This doesn't apply to consoles.

I've "linked" my PS4 Paradox games to my forum account (doing it on one appears to have done it for all of them) but nowhere did it say what doing such linking actually achieved; it certainly didn't populate the "owned items". IMO, at an absolute minimum the relevant forum and support pages should at least mention the consoles with some excuse as to why it doesn't work.

It doesn't seem to be on anyone's to-do list. The help page I linked to above has been edited several times since the console release (latest edit is June 06, 2019 17:43) and still uses language that assumes all non-Steam game are via GoG, physical disc etc. In a previous port I commented that at the absolute minimum a sentence such as "PS4 and XBox consoles are not supported at this time." would at least not actively mislead/misinform console users that follow the help/support links; that was back in March.

Note the last edit of the page linked above is now January 27, 2020 13:44 and they still can't be bothered to even acknowledge console's existence with a "not supported" sentence as I mentioned a better part of a year ago.