Thunderbird will prompt you for a password in case it is needed. In the password prompt is a checkbox where you can tell Thunderbird to remember the password, so that you don't have to type it again and again.

Barbara, you seem to be referring to the primary password needed to access Thunderbird. By design, you must enter this password once per session. If that's what you're asking about, you will either have to keep entering it or turn it off.

When you are asked for the password, does Thunderbird accept it? If so, and if you are talking about your primary password, then it must still be saved, and you do not have to enter it again in Settings.

But you also refer to "changed email" in your email provider. Do you mean that you changed your e-mail account password?

Which password are you being asked for? The primary password that provides access to Thunderbird or the e-mail account password?

Screen pics would be helpful.