Thank you for your question.
Once a judgment is rendered regarding the custody of a minor child, its terms determine the rights of all the parties involved - be they the parents and/or third parties. So, the first place to begin is a review of the judgment itself. Usually, custody and/or guardianship actions are filed where the child resides or where either parent resides, so checking the courts there is where one would want to start in getting a copy of the judgment.
Then, it is important to carefully review the judgment to determine what those rights are.
Lastly, if the judgment is unfavorable, there is a right to pursue a modification of that judgment.
Parents often file for a modification of unfavorable judgments once their circumstances have changed. For example, a parent who did not have a stable home or financial situation before might have that now and file a modification to regain custody of their child.
Generally, an attorney is required, due to the complexity of these actions. If you cannot afford an attorney, you can contact your local legal aid office for assistance. However, it is also possible to file on your own using the court's self help center, which can help you get access to necessary forms and instructions for filing.