how to remove. Hide my email address facility

System Settings > Apple Account > Hide My Email then scroll the sidebar to find the pertinent website.

Select the website and click the "Deactivate" button in the panel.

Once a Hide My Email address has been deactivated, you can then click the gear icon below the sidebar and Show Inactive Addresses. Then on that panel you can select and permanently delete any inactive address.

Use Hide My Email on Mac - Apple Support

Yes, when you deactivate a Hide My Email address, the original address is no longer being changed, but also, anything sent to that invented proxy address no longer gets forwarded to your authentic email address. If you only ever submitted an HME address to a website, they have no idea that the proxy address is not your authentic email address.

There is never any real effect on your authentic address other than to hide it from whomever you submit the HME address to. You are always free to submit your authentic email address anytime you like, even to a site to which you've already submitted a Hide My Email address. If you wish to use your authentic email address at a site that currently uses your HME address for contact, you will have to submit that email change to them.

❝The web site I am using it with does not appear in the list of email addresses❞

Some website addresses are not clearly attributable to a website's name. Most are, but others - not so much. Use the Search field if you don't easily find what you're looking for. Search by HME address or website.