all thunderbird has is your last-used password. I doubt that helps you, but you can retrieve it at - settings>privacy&security - cllick savedpasswords and then showpasswords - I doubt these are useful or they would have logged you into the account - my guess is that you may need to contact your email provider for password

You cannot reset the password of your email account using a mail client such as Thunderbird because all that Thunderbird does is use the password you tell it to use.

If Thunderbird (or any other mail client) could reset your password without you needing to know what the current password is, then anyone would be able to access your account by merely knowing your email address and requesting a password reset…

It's the email provider that hosts your email account who knows the password and may allow you to change it. It's there where you have to go (and be able to authenticate or prove your identity somehow) to request a password reset.