How can i get a modfication on a judgement

I move out of state n left my son with his father untili gt apt three weeks i return he refuse to gv my son bk n move upstate with sumbody n now the judge gv hi. Physical custody and he hasnt taken care my child ove rfive years and iam still supporting my child he has my son dirty and wearing other ppl underslothes my son os autistic and nonverbal he cries for me all the time and i dk how can. Go about getting my baby return to mei agreed to move back just so i can get my baby