How can I get rid of an email address I don't have anymore?

Hi HelpMy11,

welcome to the Apple (user-to-user) Community.

Re: "How can I get rid of an email address I don't have anymore?

I don't know where to even start finding where that address is!!"

If the old eMail address is still being used as your Apple ID log-in, it would likely appear in Messages, FaceTime, iCloud etc.

If you no longer use the email address that's associated with your Apple ID, you can change it. You won’t lose access to your contacts, purchases, or other account information:

How to: Change your Apple ID - Apple Support

and

What to do: If you forgot your Apple ID password – Apple Support

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If needed: How to: Get a verification code and sign in with two-factor authentication - Apple Support

You might need to allow 24 hours for the new eMail address to be in use.

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If the old eMail address was not used as your Apple ID:

You could begin by deleting it as an eMail account:

How to: Add and remove email accounts on iPhone - Apple Support

All the best :-)