I can't remember my password & tried to make a new one but still can't open emails.

The only password that Thunderbird uses for itself is one you can use to protect your saved email account's passwords. It does not prevent you from using Thunderbird, only from viewing the saved passwords.

If you have forgotten your actual email account password, and you have no record of it otherwise, you will have to reset it on your email provider's web site. Then you can update Thunderbird with your new password.