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

You need to disconnect your TTU account in Windows first.

Following the instructions in the Microsoft support article Manage User Accounts in Windows under the heading "Disconnect a work or school account".

Outcome

Your TTU account has been removed from Windows.