Check that little baby multiple times per day, and wash away the poop with warm water, and a gentle cloth. A little olive oil to the area can help prevent sticking, but its REALLY important to clean it often. Sometimes it takes a few days of constant cleaning, sometimes a few weeks, but they can recover perfectly well!
Check brooder temp too. Too cold can contribute to the problem.
Edit: I should have said "WIPE" away poo. You don't want to wet your chick unnecessarily.
No need to worry, google pasty butt and you will get a lot of threads and you tube videos even on how to care for chicks with pasty butt! Just wash it off and keep an eye on it! If it is really dry, sometimes you can break it apart with your fingernails, or just some warm water and a wash cloth. Most of them like the warm water. Just don't try to rubb off the umbilical cord that is a little under the vent. Good luck!
Oh yeah, I did use Olive oil on one baby where the little tiny feathers around the vent just wouldn't clean off, and they seemed like they were pulling, worked perfectly.
one of my chicks got a really nasty case of pasty butt and I warm water + paper towels didn't work. I had to ask my mother to hold the chick still while I snipped the poop off - some feathers below the tail had to be snipped off as well, but the problem didn't come back.