Duplicate issue

Hey! I am going through Section 2 lecture 20 (Duplicate and Merging) and can’t seem to get the other one to change shape with the one I am changing. For example I pressed CTRL+D to duplicate my wedge-> go to edit mode then try to change the top side say longer but the other one doesn’t change as well.
I have tried reopening the program and resetting my computer. It may be when I created the wedge that the option is gone (followed exact steps in previous chapter)
Here is a picture:

Nevermind XD It took a while but I figured out it was Alt+D not Shift+D (Said Ctrl but I meant Shift)