Counting Assigned tickets

I want to know how many tickets a group assigned to a different agent group.

In our organization, we manually assign tickets to other agents. Is it possible to create a report, wherein, you can see, which agent (or agent group) assigned how many tickets, to which agent (or agent group) in your organization. 

I think this is the type of custom attribute that I would need to put in place, but I'm not sure how to fill each variable.
IF ([Changes - Field name] = "group_id" AND [Changes - Previous value]!=NULL AND [Changes - New value]!="0") THEN [Update ID] ENDIF

Thanks!