Hello, I'm a soldier stationed at Ft. Hood Texas. I want to file Joint Physical Custody in the city of Columbus, Georgia. How do I go by doing that?

My daughter is 10 years old and I talked to her mom the other day and she had agreed to give me joint physical custody of my daughter. She will not argue or dispute this issue at all. She is 100 percent on board with this. I'm at soldier stationed at Ft. Hood, Texas and would like to know how to get this started. I already have the paperwork to legitimize my daughter which I know is the first step. I don't have a clue what to do afterwards. Can someone please help me.