Menus: Editing an existing sidebar menu
If you have an existing sidebar menu you need to edit, first open the backend editor of a page that contains the sidebar widget in question, and find which "widget" is being pulled into the page.
Here is an example of a widget menu displayed on the live frontend webpage.

Below you can see the widget on the backend of your WordPress page. Edit it to see which widget is being used.

Below you can see that the widget sidebar being used is called "Academics."

Now go to Appearance > Widgets in your left dashboard menu.

Then open up the Custom Sidebar titled "Academics" (or whatever the widget you're looking for is called) and take a look at the content within. Sometimes, it's regular HTML being added into the widget. If so, edit the content, then save the Custom Sidebar.
If the Custom Sidebar content points to a menu (see below for how it points to menu="Academics"), open Appearance > Menu.

In the Menu section, select the menu you're looking for (in this case, "Academics"). Click Select, and the menu will appear.
Make the changes that you need and save your menu. Then go to the pages that contain the widget that points to this menu and, at the top of each, click Hummingbird > Clear Page Cache to ensure your new menu is visible to all users.

Keywords: menu, menus, sidebar, edit, editing, cache, widget, widgets, appearance