File a petition in the court that granted the divorce and terminated his rights
I am not intending this to be legal advice, because I don't know the particulars of your situation. Call me if you would like to discuss this or other isues.
While I realize you wish to proceed on your own, despite coming to an attorney forum to seek advice, your best bet may be to sit down with a local attorney and pay for at least a consultation on how best to tip toe through the legal process without any training.
Sign up to receive a 10-part series of useful information and legal advice about the divorce process.