If you don't get a login prompt, you already have an account connected.
You can log into into https://help.ea.com/en/ via the Xbox/PS4 login options. Once you're logged in here you can go to Accounts > Order Management, and it'll try to transfer you to the main ea.com site, and on this page you should see the email address for the linked EA account.
You can log into Origin.com then go to your profile (in the bottom left) then Edit on EA.com (in the top right). On this page you can scroll down and see your linked accounts.
If you already linked Twitch to the wrong account, you can unlink it, then link the right account, using the steps here: https://help.ea.com/en/help/apex-legends/apex-legends/apex-legends-and-twitch/