When trying to sign in to my Thunderbird email, I get the message to use my password, but I don't know of one so how do I fix this?

Please quote the message that's asking for the password, complete and verbatim, or post a screen shot. The only time Thunderbird itself would ask for a password is if you have locked access to your Saved Passwords. That feature can be found at <Settings | Privacy & Security | Passwords | Use a Primary Password>. If it's not that, it can only be your email provider asking for your password. You might find it in the Saved Passwords area I described above. If it's not there, and don't have it recorded somewhere, you will probably have to reset your password on your provider's web mail page.