Most court cases do not set any precedent. If you think the judge made a legal mistake in your case, you can appeal regarding that specific legal question.

The appalete court can then issue a ruling on that specific question of law. If they find the lower court was in error, they would typically send it back to the lower court to redo under the new guidance.

Sometimes the specifics of the case do interfere with the appelet court's judgement, but the entire system is set up to minimize that.