When it comes to custody cases, you can ask for a paternity test if parentage hasn’t been established. This mostly occurs when you want to find out if the individual assumed to be the father of your child is their biological parent.
Unfortunately, if there is already a court order that declares someone is the father of your child, it will be too late for the test. In this case, you can file an action to terminate paternity, depending on your state. However, the law can declare a person the legal father even when they aren’t the biological father.