It depends entirely on where your file has got to. Before it is filed with the US authorities, most things can be corrected. Afterwards, nothing can.
Before your application is filed
Tell us as soon as you notice. If your file is still with us, at payment received or verification, we correct the information and carry on.
Contact us with your file number and say exactly what is wrong and what it should be. For a group, say which traveller.
After your application is filed
Once the application is with the US authorities it is fixed. Neither you nor we can edit it, and there is no correction procedure.
If the mistake is significant, a new application with the correct information is usually the answer, and that means a new application fee. Contact us before doing anything, so we can look at your file and tell you whether it is necessary.
What counts as significant
A wrong passport number, or the details of a passport you will not be travelling with
A misspelled name, or first and last names the wrong way round
A wrong date of birth
A wrong country of citizenship
These have to match your passport exactly, because they are checked automatically at check-in and at the border.
What usually does not matter
Travel details are not fixed to the authorization. A change of flight, hotel, arrival date or address in the United States does not require a new application, and does not need to be reported to us.
Your US contact details and your emergency contact are the same: helpful when given, not a reason to redo anything if your plans change.
If you renew your passport
A new passport always means a new authorization, whatever validity was left on the old one. The same applies to a change of name or of citizenship.