Even if you do nothing, chicks will eventually start using the perch.
At five to eight weeks, the instinct to want to be on the highest surface in the coop is extremely strong. You can increase their interest in roosting on a perch by raising it to a more inviting height of around 24 to 30 inches.
You may also encourage them to use the perch by placing them on it when it gets close to dark. Placing them close together will increase their feeling of security.
If they seem agitated at being on the perch, place your hand lightly on their backs and heads with slight pressure to lower their heads horizontally level with their bodies while making a comforting shhhing sound. Do this with each chick alternating between individuals until they quiet down and remain still.
With this training , chicks will usually roost on their own within a couple of nights.