Please refer to Integrate with other apps—Survey123 for ArcGIS | ArcGIS and https://community.esri.com/groups/survey123/blog/2016/07/30/understanding-survey123s-custom-url-sche... to get started - you will create the URL in the popup of a feature in the Collector web map.
Awesome! That worked, though I had to make two separate links, one for the web app and another for the field app. And I had to use the long form of the survey URL. I could not use the shortened form that is given within "Collaboration" tab in the web app builder.