If you signed in with the credentials of the primary account then you should have seen something similar to the following:

If:
- you saw the Manage accounts tab but the email address to delete was not shown then it it likely linked under a different primary account
- the Manage accounts tab was not shown then you signed in with a secondary account, try again with the primary account
Otherwise post back here and I will flag the thread to the forum team as they are best placed to take this forward.