Wiktionary
vb. (context idiomatic English) To be in charge, to be in control, as of a business, political organization, or other group.
Usage examples of "hold the reins".
I remember when he put me up on the seat and let me hold the reins.
Tirsik could partly clean the stall, but none of his stable boys, and no one else could so much as touch the palomino, only hold the reins once he was bridled and saddled.
We kept alternating riding and walking, except I walked more than I rode, a lot more, and I had to hold the reins when Alasia rode, not to keep her from riding away, but to keep Gairloch from bucking her off.
JD's back was turned, Zandy was explaining how to hold the reins, and a groom was adjusting her stirrups.
Hands still too numb to hold the reins, Rakio clasped them round the horse's neck.
While galloping, the bearer had held it nearly horizontal, like a jousting-lance, in his left hand, while using his right to hold the reins.
The outside men would hold the reins of the horses ridden by the three who'd go in.