Because Shopify changes the theme of the Navigation tab, it leads to an error on the Menu import process. You can't see the Arena Menu import button to import your sample menus.
In order to do that, please follow:
When the app opens the Navigation tab, please click on Main Menu, you will see Arena Menu Import button there. Click Arena Menu Import to process import menus.
Find more detail with video guide: https://drive.google.com/file/d/1YuZClwW2O68YYB9jaCh1Yqw4mzIFn7-q/view?usp=sharing