If your parental rights were terminated as part of a court action, the only way to change that result is to appeal that determination to a higher court. It cannot be reversed once the termination is complete unless you have a court overrule the court order terinating those rights.
If the adoption was more than one year ago, you will not be able to challenge the adoption. Even a motion to vacate would not be helpful.
Even when you do everything the state wants you to, children may not be returned to your care. The state may feel that you took too long to complete services or that you jumped through the hoops. Courts also have to look at the child's best interests too. Federal laws really put the pressure on achieving permanency as early as possible.