You should be able to use this site to scan for Among Us files on your computer, to confirm you have it, like I do, but the site doesn't register that I bought Among Us from it. If it sees the files, it redirects you to where you can update it. I think it should be like that.
It'll say you own the game at the top of the page if you've bought it.
Alternatively, you can update the game from Steam or the itch.io app.
https://itch.io/app