Go to Appearance → Menus, select menu for editing
You need select element for multicolumn
and add next classes (you can add multiple classes like “.sub-col-3 .sub-full-width”)
Numbers of column
.sub-col-2
.sub-col-3
.sub-col-4
.sub-col-5
.sub-col-6
Size of dropdown menu
.sub-full-width
Align for dropdown menu
.sub-align-left
.sub-align-center
.sub-align-right