big flat tray of dirt or let them out. Chicks / chickens don't run away when you let them out, they'll follow you a few feet basically. Is there dirt next to the coop ? if it is safe from predators, just let them out.
For a dust bath container you can use just about anything, we use an old galvanized tub, I've seen an old child's sandbox, old tires, child's swimming pool or, depending on your climate and soil, nothing but a dry area of dirt in the run.
In ours we use a mixture of peat moss and wood ash. Sand is also popular.
Do they free range mostly or are they confined to a run? That will determine the kind of dirt bath you need to create.
Years ago, when I determined my flock needed a dirt bath, I chose a nice spot on the hillside under the shade of big pines. I filled it with loose soil, sand and wood ashes. My chickens ignored it completely.
Not long after that, I created a squash bed near their coop and run. It was in full sun for the squash to grow. Guess who loved digging holes and dirt bathing in the squash bed?
A good dirt bathing station will first of all be in a nice sunny, warm spot. It should be well drained so it doesn't fill up with mud during wet weather.
Loose soil is best. You can add sand, peat moss, and wood ashes to create a nice loose material that gets well into all the feathery nooks and crannies of the chickens' bodies.
It should be in a safe, protected spot so chickens can relax and not feel vulnerable to predators. It should be shielded from the wind and hot sun in summer.
A dirt bath in a run can be a dug out hole filled with sand and peat moss. My runs are sand. My chickens dirt bathe in holes they dig out themselves right in this sand. They do, however, choose spots that usually see sun during part of the day. Sun bathing and dirt bathing go hand in hand, dirt conditioning the feathers and sun creating vitamin D absorbed into the feathers.
Dirt bathing is an essential facet of a chicken's health. Don't deprive them of it.