dispute a judment

Disputing a judgment, after it has been entered, is difficult, because you not only have to show a "meritorious defense," which means that if you get back into the case you have at least some real chance to win something, and you have to explain why you didn't respond to the lawsuit or proceeding that led to the judgment in the first place.

If notice of the judgment is the first you knew about anything like this, that's a good reason to dispute it, because you are always entitled to notice and the opportunity to be heard before a judgment is entered.  This is the largest part of "due process" as guaranteed by the Constitution.  But you must act on this immediately, because the longer you delay in asking the court to reopen this, the harder it is to successfully explain the delay.