Our tasks are drawn from a common pool, I am trying to track the close rate for each user. To do that it seems I need to reassign the task to the user editing/closing it. Salesforce support indicates this is possible, but I have no idea where to get start. Anyone have any ideas how to go about this?

*We are in Salesforce classic if it matters. 

Our tasks are drawn from a common pool, I am trying to track the close rate for each user. To do that it seems I need to reassign the task to the user editing/closing it. Salesforce support indicates this is possible, but I have no idea where to get start. Anyone have any ideas how to go about this?

*We are in Salesforce classic if it matters.