Your TTU account is listed in Windows 10 under Settings > Accounts > Email & app accounts. You would like to delete it. However, if you click the "Manage" button you are taken to the eRaider sign-in page. You're unable to sign in because your eRaider and TechMail account is either disabled or deleted.

You need to disconnect your TTU account in Windows 10 first.

1) Go to Settings > Accounts > Access work or school.

2) Click once on your TTU account.

3) Click the Disconnect button.

Outcome

Your TTU account will be removed.