Most of the time yes it will resolve itself. If it's caused by old or moldy feed, then you'll need to throw that out and get some fresh feed. Medicated starter for chicks seems to help too, but everyone doesn't feed medicated and they do just fine. I'm not knocking the Dumor feed, but I have heard a LOT of complaints with pasty butts from folks that feed that particular brand to new chicks. Don't know why, so please don't take it wrong.
I also feed mine plain yogurt with active cultures to build up their intestinal bacteria and to help their immune system fight the diarrhea. A little scrambled egg gives them extra protein as well to help them heal, but try to get them to eat mostly their starter crumbles so they get balanced nutrition. The ACV that speckledhen advised is excellent advice and you can add a clove of garlic in as well to build up immunities and help them utilize their feed better.
You can use either baby oil, or olive oil to put around their vents to help keep the poop from sticking and stopping them up.