If you don’t see the fields to assign an action to someone, your user role doesn’t have permission to access them. You or your admin need to update the settings to make these fields visible.
From the left menu, click Admin.
Under Site, click Mandatory Fields Configuration.
Click through the pages till you find the Action Owner and Responsible person under the Field Name column.
Click the edit icon to the right of the trigger.
Click the Filter by Roles drop-down box.
Select the roles to give access to the fields on actions.