They "walk" them down.

A light wagon, two mules to pull it, lots of grain, some water and supplies, are what you need.

On sighting a band you simply walk your team after them, walk all day and day after day, never giving them a rest.

Keep their attention occupied and they will neglect to feed or drink.

Gradually they become accustomed to your nearer presence, and finally you can get up quite close and even drive them into your camp, where your companions are ready with snare ropes to secure them, or at least the particular ones you want to catch.
Prince, a horse I used to ride when mustang hunting, once accidentally gave me a severe tumble.