You definitely don’t want to force the chick to eat. First you need to make sure the chick is warm enough. A cold chick can’t digest food and it will sour in the crop, and usually the chic does not survive. You didn’t mention the age, but unless he has most of his feathers, he needs a heating pad, set on low, under the container you have him in. You need to make a brooder – most people use the small clear plastic boxes sold for small pets. He should be warm and alert, and then you can try to entice a feeding response. You may have to feed him drop by drop. Don’t make the formula too thin or he is more likely to aspirate. You can try using a spoon so you can get it into his beak. Put a drop in his mouth and see if he swallows. If he gets a taste or formula, he may begin to eat willingly. If this is a feathered chick who should have already left the nest anyway, you can try offering some solid foods like seed, and soft foods like cooked rice & mixed veggies. You can probably find videos online showing how to fee a reluctant cockatiel chick.
You also need to remove the nest box so the parents don’t lay eggs again right now. They should be rested for at least 6 months before you return the box. But if this is the best they can do with chicks, it might be best not to breed them again. Or next time, pull the chicks for handfeeding before they are too old to accept it.
Thank you for asking Lafeber,