This document explains how to get the user's name in the activity filter when the user updates the assignment group field in the incident form

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1. In the activity stream filter, you need to check both "Assigned to" and "Assignment Group" to have them appear in the stream.
2. In order to do that, you need to make sure the fields are included in the value of the following system property - glide.ui.incident_activity.fields. You can access this system property by plugging in your instance name to this link: 
   https://<instance-name>.service-now.com/nav_to.do?uri=sys_properties.do?sys_id=99abcc98c611229201e61dd0aa031339
3. Once you have both the field names included in the values for the property, clear the cache of your instance by entering "cache.do" in the filter navigator. 
4. Navigate to any incident form and change the value of the assignment group to see the activity field displaying who reassigned.