Assuming the password became corrupted, and that you know the real password, you could select settings>privacy&security, click 'saved passwords' and then 'show passwords' and rightclick the account rows and click 'edit' and enter the password. Another option is to highlight both rows (incoming and outgoing) and delete them and then let Thunderbird prompt for the password.

Unfortunately neither option worked for me. The first option there was no passwords showing so I couldn't do anything with it. The second option I'm not sure where I'm supposed to delete "incoming" and "outgoing" but Thunderbird already prompts me everytime for a password, but tells me it's the wrong password even though I know it's the correct password because I wrote it down and have had it for several years. I'm wondering if it has something to do with the server because it's showing incoming and outgoing servers as ATT which I no longer have anymore.

You have to create a secure mail key, then remove the entries in Saved Passwords in Settings, restart TB, enter the key when asked for a password.

https://www.att.com/support/article/dsl-high-speed/KM1010523/

How do you create a secure mail key? I have no saved Passwords in Settings...for some reason it never saved any passwords.

Do I need to create a secure mail key with my internet provider Cox Communications?

Secure key information is in the link in my first reply.

Create the key with the account provider, which might be different from your ISP.

I understand now. I should have never switched to Cox Comm. since they are not on the list of account providers. One of these days I will switch back to AT&T. At least I know now what was causing the problem. I thought I was losing my mind and somehow didn't have the correct password.