You chose not to identify your state, and expungement laws are different in each state, but expungement laws typically require you to go back to the sentencing court.

I'm going to assume this is Texas, and move the thread to the appropriate forum, in which case you would go back to county were the sentence was issued:
Quote Quoting Texas Code of Criminal Procedure, Art. 55.02. Procedure For Expunction.
Sec. 1. At the request of the defendant and after notice to the state, the trial court presiding over the case in which the defendant was acquitted, if the trial court is a district court, or a district court in the county in which the trial court is located shall enter an order of expunction for a person entitled to expunction under article 55.01(a)(1)(a) not later than the 30th day after the date of the acquittal. Upon acquittal, the trial court shall advise the defendant of the right to expunction. The defendant shall provide to the district court all of the information required in a petition for expunction under Section 2(b). The attorney for the defendant in the case in which the defendant was acquitted, if the defendant was represented by counsel, or the attorney for the state, if the defendant was not represented by counsel, shall prepare the order for the court’s signature. ...