How can I get a hearing to seek custody when my ex has jurisdiction legally?

My custody case is in Pennsylvania due to the uccjea law. PA was deemed the home state of our son. My state released jurisdiction over the first custody order in the divorce that gave me full custody. PA judge gave my ex primary custody, and I didn't get any visitation or anything. I want my son to live with me in Mississippi with his other 4 siblings. My son is only 9, but he wants to be with us. How do I get a hearing in PA to seek custody, and I don't think the PA judge used the right due process. I have never lost my parental rights. I originally had custody in Mississippi until my ex took our son to PA and would not return him, where he received jurisdiction illegally.