Final answer:
If the desired amount of lift is not achieved using a single-process color, the most appropriate step would be pre-lightening the hair. Color remover may be used if there is a need to remove color from the hair. Toning and heat styling are not directly related to achieving lift with hair color.
Step-by-step explanation:
If the desired amount of lift is not achieved using a single-process color, the most appropriate step would be pre-lightening the hair. Pre-lightening involves using chemical lighteners, such as bleach, to lighten the natural pigment of the hair. This allows the color to penetrate and achieve the desired lift. After pre-lightening, the color can be applied to achieve the desired result.
Color remover (option A) may be used if there is a need to remove color from the hair, but it is not necessarily required to achieve lift. Toning (option C) is used to adjust the tone of the hair color and may be done after achieving the desired lift. Heat styling (option D) does not directly contribute to achieving lift with hair color.