For Admins only
If you are a Canvas Administrator, you can restore deleted assignments. Read this article on How to check if you have administrator rights in Canvas. The deleted items - Assignments/Quizzes/Discussions/Surveys are restored along with the responses or submissions into its course respectively.
In Global Navigation, click the Courses link , then click the name of the course  in question.
Modify the course URL
Check the course URL. Add /undelete  at the end of the URL, hit enter.
View Restorable Items
A list of restorable items will appear for that course.
If you need to restore your deleted item, click the Restore button.