Child support liens are typically placed by a child support office or other judgement creditor on an NCP’s real estate property such as a house when that NCP owes child support arrears. The idea for the lien is that the lien will help ensure that proceeds from the sale of the property will go toward paying off the arrears owed to the CP. But how does one remove a lien off  their property in order to sell it?  Simple answer: pay off the debt! Next simple answer: negotiate a deal with the CP over the arrears to help remove the lien on the specific property in question. Hiring a property law attorney can help but an NCP could also seek out a family law attorney (child support liens are one of the few areas outside the divorce process where property law intersects with family law).
Oh yes, there is the third bad option of just trying to sell the property with the lien still on it. But this is probably a bad idea. Besides, potential buyers will likely stay away as they would not want to inherit an NCP’s child support drama.