This should grab the first person assigned to the case:Case Search
Criteria tab > Standard subtab
Select the Filter: System Notes Fields…, and on the new pop-up window choose: Field, for the Field selection: any of: Assigned, click Set.
Results tab, Sort by: Number, click the button Remove All
Under Field column, add in Number, on Summary Type column, choose: Group
On the next row Under Field column, add in System Notes Fields…, and on the new pop-up choose: New Value, click Add
On the same row (System Notes: New Value), on Summary Type column, choose: Minimum, and on When Ordered by Field column, choose: System Notes Fields… on the new pop-up window choose: Date
Click OK
Save