Go to the Follow Ups Page from the Fundraising Module>Sponsorships.
Click on the Edit icon on the left side of the grid next to the task. In the pop up window, toggle the Completed button to YES, enter the date the task was completed and any comments. The user who updates the task will automatically be entered in the Completed By column. The grid can be filtered using the Edit Column Settings on each column and then the list can be exported to Excel using the Actions menu.