No red color to it? Blood?
IF possible get this this morning.
It's worth a try.
https://www.tractorsupply.com/tsc/product/nutri-drench-poultry-4-oz-2202048?gad_source=1&gclid=Cj0KCQjw0MexBhD3ARIsAEI3WHIVa66xrQgOPeGhpgOpagtPa3MS0ooEsUyzXd1dyYiL0BxbSqmslYsaAugIEALw_wcB
The Marek's vaccine does not prevent the disease.
What exactly has the chick been eating?
How long have you had the chick?
ACV isn't going to help. Plain water would be better.