Okla. Stat. tit. 12 § 1177
The answer of the garnishee shall in all cases be conclusive of the truth of the facts therein stated, with reference to the garnishee's liability to the defendant unless the judgment creditor shall within twenty (20) days from the receipt of the garnishee's answer, from the date of the deposition of the garnishee, or from receipt of the garnishee's answers to interrogatories, whichever is later, serve upon the garnishee or the garnishee's attorney of record personally or by certified mail, return receipt requested, a notice in writing that the judgment creditor elects to take issue with the garnishee's answer; in which case, the issue shall stand for trial as a civil action in which the affidavit on the part of the judgment creditor shall be deemed the petition and the garnishee's answer the answer thereto. If an issue for trial shall be joined between the judgment creditor and a garnishee resident in another county other than that in which the action is pending, the court may, on motion, change the place of trial of such issue to the county of the garnishee's residence. The judgment creditor may, in all cases, move the court, upon the answer of the garnishee, and of the defendant, if the defendant shall also answer, for such judgment to which the judgment creditor shall be entitled, but any such judgment shall be no bar beyond the facts stated in the answer.
Okla. Stat. tit. 12, § 1177