Blocked nares could indicate an upper respiratory disease, but it could also be something as simple as having mushy feed clogged in there. If there is any chance that it is a respiratory issue you could try flushing the nare with saline in a syringe ( no needle ) and then start the bird on antibiotics. If you've been feeding a mash or wet food, you could try using the tip of a tooth pick, to very gently remove the obstruction. It is safer to have someone hold the chick while you do this.
Examine the bird well before making a decision as to treatment and have a good sniff of its beak. Often coryza or MG will give a foul smell. Being as the chick is only a few days old foodstuff wouldn't have had a chance to sour.