I am trying to enable it using plug ins but its failing.
Leveler is available in Effects > Distortion.
Leveler used to be a primary effect, but was demoted because of the distortion it causes. It was kept because of its ability to easily create theatrically distorted voices such as Air Traffic Controller and Taxicab Voice.
Effects > Limiter does many of the same jobs without the distortion. Limiter is used in the Audiobook Mastering Suite. It depends on your application.
Koz