Which password? If it's one for your email account you need to work with your email provider to reset it. However, do check under '''Tools|Options|Security|Passwords→Saved Passwords''' It may be stored there. If it is stored there more than once, then Thunderbird will be asking you for it since it doesn't know which one to use. If it is Thunderbird's Master Password, then we can find instructions to allow you to reset it, but along with all the stored passwords.