Yes, you can delete or edit current assignments in the Manage Assignments application under the Administration tab.
On the first page, select the user you need to recall the assignment for. If there are multiple users or you are unsure how many have the assignment, you can always click Select All Visible and sort them out later in the process. Then, click Continue.
The next page will list every pending assignment for every user that you selected. Check the box next to the assignment you need to edit and click Continue.
The final page will list the assignment details for each assignment based on the users and courses/activities you selected in the previous steps. Check the boxes next to all assignments you need to edit or delete. If this is a long list, you can select all by checking the box in the top left corner.
Once the desired boxes are checked, you can choose either Edit or Delete.