I have put in a forwarder from gmail but not all email are being redirected

I'm not exactly sure what you're asking for. Any redirection of messages from the Gmail account to your new account happens on the server. Thunderbird is not involved in that at all.

If there are any more details you haven't mentioned yet, now would be a good time to post them.

I use Thunderbird for reading all my emails, So I wanted to send all the emails from my old email address to my new one using Thunderbird.

As said before, that's something you'll need to do on the server. It has got nothing to do with Thunderbird.