Answer:
Influence.
Step-by-step explanation:
The power of effecting change in someone or something is known as influence.
In English language, influence can be defined as the power to affect or change an individual, group of people or an inanimate object without necessarily having to force the change to occur, happen or take place.
For example, President Donald Trump used his influence to reform his country's health insurance policy.
Also, John has remained under the influence of his physical health instructor.