You would have to file a motion requesting that the agreement not be approved on grounds of fraud, mistake, illegality, coercion or undue influence.
If you argue mistake, then you would have to show that the other party knew or reasonably should have known of your mistake. If you argue fraud, you'll need to show that not only were you tricked into signing, but that you could not have reasonably discovered the other party's deceit in advance. If you argue coercion or undue influence, you would generally need a third party witness to testify to the pressure you were put under. Finally, if you argue illegality, you need to show the precise violation of law.
Otherwise, the judge will enter the settlement.
Hope this helps.
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