Rehoming is when adoptive parents decide to disrupt their adoption and find new adoptive parents or guardians for their adopted child. This is most often done due to behaviors that are beyond their ability to parent. Most adoptive parents complete a rehoming through the court system with an appropriate assessment of the new home. There have been cases when an adoptive parent simply transfers guardianship of their child to the new parents and has little to no knowledge about the family.
This is a very controversial choice and I would recommend working with a social worker, a lawyer, or other official to make sure things are done in a safe and legal manner for all involved.