While seated on a bench, place a ribbon/flat band behind your head. Straighten out your back while still holding onto the ends of the band
Gently extend the arms till the band starts applying force onto the neck muscles. Maintain the arm position.
Allow the chin to slide forward, before pulling the head back. The neck in the "back" position should be straight and elongated.
Guia do Exercício Cervical Extension Band | MuscleWiki