After importing but you can't find a menu, you can fix it by Navigate to Appearance → Menus and select the Manage Locations tab. In this tab, set the appropriate menu types. Save your settings and check it.
- Go to Appearance > Menus
- Click Create a new menu. Enter a menu’s name and click Create Menu
- Check the menu item in the boxes in the left column, click Add to Menu to add items to the menu, and drag/drop to arrange them.
Click Save Menu
Now assign your newly created menu to appropriate locations