@Cookie84monster Just to be sure, you ordered the Founders Edition and not the Premiere Edition, right? Because the additional buddy pass was also only for Founders.
EDIT: After checking your username via Stadia I assume you're "Cookie84monster#8437" which means you're not a founder and don't receive buddy passes. (at least for now)
As @Bahlor explained this was a feature for Founders only currently. If you have a Founders Edition then there is nothing to do, you will see the Buddy Pass available in the Stadia app, if you have a Premium Edition account then no such joy currently.
If you do have a Founders Edition account (you'll know because your account name won't have a bunch of numbers after it) and you do not have the Buddy Pass invited available then reach out to Stadia support and they can investigate the matter for you. https://support.google.com/stadia/contactflow