Delete all data from the previous account and make a new one. Report the troll to moderators. Consider never visiting that place again if the mods won't help you with the harassment.

If the troll doesn't have access to the forum's server, then all you have to do is learn some opsec and be aware of what you share with strangers on the Internet.

If the troll does have access to the server and you absolutely need to visit the forum (which I'd advise not to in such a case), then in addition to what has been said above, use VPN with a hardened browser or Tor to access the forum.

You're also doxing yourself on Lemmy. Be careful. Linking to the person whose doxing you is effectively doxing your lemmy profile.

I don't mean to be a dick, but if a troll is able to pass your information out, you need to adhere to better personal information security practices.

Doxing is legally classified as harassment and is a criminal matter; contact law enforcement. Even if they don't do anything you'll get in their records so when your harasser tries to do something (like swatting) they'll know that something is up.

For the future, maybe search your name and see if there are any results that are you. Then try name and your city, see if there is anything.

Besides contacting the admins, there's nothing you can do at this point. Prevention is better than cure when it comes to internet privacy