To lengthen the lower 1/3 of the face could be achieved with a chin implant or better yet a sliding genioplasty with stacked bone to increase the vertical height,. but really, you woudl need an exam before even these are considered an option.
The best way to lengthen the lower third of the face is through orthognathic surgery. This should be performed by an experienced oral and maxillofacial surgeon, facial plastic surgeon or plastic surgeon wtih specific training in orthognathics or craniofacial surgery. Many surgeons will take a series of measurements to decide the best way to proceed.