Forwarding yahoo emails to thunderbird

My computer windows 10 went black screen last week and when I got it back up my password for one email (yahoo) was lost. Even thou the log in is att,but yahoo is the provider or vis-versa. After many tries with att to login, I got locked out. At some point I was told that I could get in from yahoo. Yahoo gave me a key code to get to my emails which was good. But I have been using Thunderbird to read, send,reply, save in folders,etc.

The problem is I still don't have a password to put in TB in order to download the emails to my desktop. When I try to change the password in yahoo, i get sent to att and I have the same problem, it will not accept the key code and does accept my answers to the (2) questions(I know they are correct), and will not send a text to my cell phone(which i can see it's correct by the last 4 numbers they have listed). Att will not help because the email is a free email I have had since 1980"s when I was working for Pacbell.
Any Help would be much appreciated,
Thanks