CSV contact import is missing
Contact CSV export works properly. Unable to locate the "File import" button to re-import them, per: per https://help.yahoo.com/kb/att/new-mail-for-desktop/import-export-contacts-yahoo-mail-sln28832.html
The import is missing in both yahoo.com and att.net mail accounts.
Andrew Park commented
I had to import all my contacts into Google, in order to transfer them all to Yahoo, then I had to delete them all from Google. Why did I have to use one of Yahoo's competitors to get my contacts into Yahoo?