Deleted Resource Showing Up in Reports

Hello- I am new to the Organizer, and I started out just by messing around to explore how it worked. I added a few resources and marked some assignments complete that I do not want actually showing up on my reports. But after I went back and deleted the resource from my scheduler, the “competed” assignments still show up in my report for the week. Is there any way to go back to a specific day and delete items from that day? Or some other way I can get these fake completed assignments off my report?