How do we go about requesting that games be added into the completionator? I buy random steam codes from websites like Fanatical and Humble Bundle that are more 'obscure' I guess is the best way to put it.

I'm new to this site, so any help would be greatful :]

Under "Collection" you'll see "Item Requests", then you can put in the name and URL and other details. They'll be added within a few days, usually.

If you start typing the name in when adding a game to your collection and nothing comes up, it will also show a link to the Request page. Either way works!