You will receive the "Good news! You already have a Code.org account that uses..." message if you're attempting to log into your account using a SSO option, without the corresponding account previously linked.
If you receive this message, use the email and password option to log into your existing account - not the "Continue with..." SSO button.
If you do not remember your password, you can request a password reset.
Note: Many schools block our emails - including password reset emails. If this is the case, please email email@example.com and we can assist.
Once logged in, go to your Account Settings page to link the appropriate account.
Using Google as an example:
Scroll down to the "Manage Linked Accounts" area and click on the "Connect" button in the Google row.