MOVE BUTTONS BETWEEN MENU & SUB MENU:

Move buttons to a sub menu by first, clicking on the menu buttons tab and simply drag and drop them to the sub menu.

You can do that simply by dragging and dropping the buttons in the empty spaces below the menu buttons. This will create sub menus that will open up when hovering over them.

Here is how to move buttons between menu and sub menu:

Step 1: Click the menu buttons tab .

Step 2: Hover over the desired button. 

Step 3: Click and hold the button. 

Step 4: Drag it into the desired location below the main menu to create a submenu.