Hi John,
I assume you are meaning the Hide My Email function on your iPhone, and are wanting to delete an email account you have created for a company which you no longer wish to receive emails from.
There are two ways of doing this, depending on how the email was created. The first steps are the same: Open settings and click on your name at the top. Then go onto the iCloud section underneath subscriptions. Then click on Hide My Email directly underneath Private Relay (Beta).
If you manually created the email, select the email from the list and tap "Deactivate email address" in red, then Deactivate.
If the email address was created automatically, tap on the app/website that is using it from the list, then tap "Manage settings" at the bottom. You should see a screen pop up with a list of all apps using your Apple ID. Click "Edit" on the top right and then scroll to the app you wish to stop emailing you and tap the red button on the left of it. Then press the delete button which should've appeared on the right of the app, and finally, press "Stop using" to remove this email entirely.
Hopefully, this has helped, if not please do not hesitate to reply and let me know what's going on.
Have a pleasant rest of your day.
Will