Mo. Rev. Stat. § 558.008: Revocation of a fine.

A defendant who has been sentenced to pay a fine may at any time petition the sentencing court for a revocation of a fine or any unpaid portion thereof. If it appears to the satisfaction of the court that the circumstances which warranted the imposition of the fine no longer exist or that it would otherwise be unjust to require payment of the fine, the court may revoke the fine or the unpaid portion in whole or in part or may modify the method of payment.