[hold] the reins

to be in charge of a particular company, organization, etc.

The idiom "hold the reins" finds its origin in the literal act of controlling a horse by holding the reins. The reins are the straps attached to the bit in a horse's mouth, and they are used by a rider to direct and control the horse's movements. The phrase has been metaphorically extended to indicate control, authority, or leadership in various contexts beyond horsemanship.

As the CEO, she holds the reins of the company, guiding its strategic direction and ensuring its success.
The coach firmly holds the reins of the team, implementing effective training programs and leading them to victory.
With his expertise and experience, he holds the reins of the project, overseeing its execution and ensuring its timely completion.
As the parent, it is important to hold the reins of discipline and guidance, shaping the development of your children.
The conductor skillfully holds the reins of the orchestra, directing the musicians to create a harmonious symphony.