If your account is IMAP, you should simply be able to set up the connections for IMAP and SMTP in the fresh Thunderbird, and 'subscribe' / sync each folder to see the messages from the server. However if your Thunderbird setup was POP, or you stored a lot of messages that had been fully downloaded and saved in local folders, then you would need to connect Thunderbird with your old profile. See this article for details of ways to do that https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data