Hi randee,
You can accomplish this change by downloading the Survey123Connect for ArcGIS desktop application, downloading your survey there, and then modifying it by taking off the 'yes' in the required column of the spreadsheet for the zip code question. Note that republishing it will mean that the default web viewer for the form will no longer work; however, a different webform, accessed from the globe icon in Survey123Connect, should work (it's currently under development, but able to handle forms already published via the website).