He should have an order from the court that put him in jail. Go to the clerk of court for that court and ask to see the last order on the docket for his case. They will help you find it. There will be a purge amount and a place to pay it.
If that doesn't work contact the attorney representing his ex. You can find that information on the contempt papers that were filed. Look at the last page near the signature. The attorney representing the ex will be happy to tell you where to pay the purge and how much it is.
Before you do it refer back to my advice on the other post. Or better watch Judge Judy. I know you care about him but you are going down a bad path. Good luck anyway.