What steps does a parent need to take to get a requisition order from the court to keep a 17-year-old from moving out in Texas?

No court order is needed. If the child leaves, you file a runaway report with the police. A CRO is unlikely to prevent a 17-year-old from leaving the state, but it will allow authorities to take the minor into custody and return them to their parents or legal guardian. Contact the office of the clerk of the family court in the county in which the minor lives or the local office of domestic relations to obtain specific information.