You will need to fill out this set of forms to file a motion for change in custody in Ohio, officially called a "Motion for Change in Allocation of Parental Rights and Responsibilities." You can only use these forms if you have an existing custody order. These forms should be filed in the court where the existing custody order was made. In the case of divorced parents this is typically the domestic relations court and in the case of parents that were never married this is typically the juvenile court.
Be sure check the court’s website to make sure that you have all the forms you need. Some courts may have additional local forms that you will need to file.