If you have already made an assignment in a course and you want to reuse that assignment either in the same course or in a new course then you can duplicate it.
Navigate to the course where you want to create the new copy of the assignment.
Click "Create assignment"
Choose "Copy existing assignment" at the top of the page. Circled in green below
Select which assignment to duplicate / copy from the drop down menu
Give the copy a new name
Select whether or not to copy deadlines
What will be copied:
Deadlines (if you select that they should be copied)
What is not copied:
Submissions / hand-ins