How an assignment can be edited?

 Assignment details such as the assignment description or due date can be edited at any time.

  Click the module access icon > Academics > Assignment to open the All assignments page.

1. Select the subject for which the assignment was given.

2. Click the title of the assignment.

3. Click the Edit button and make the necessary changes.

4. Click the Update Assignment button.

For more clarifications, please watch this.