Add, remove, or edit menu items in your online storeShopify Help Center
Go to Navigation to create a menu.
Click Add menu to add new or choose any items below the menu to edit.
Write the menu's name, then choose Add menu item.
Write the menu item's name and choose the item in the dropdown box > click Add.
1. Go to Themes > Customize.
2. click Header section > Menu Settings, and make necessary changes.
3. Save the settings.
https://help.shopify.com/en/manual/online-store/menus-and-links/drop-down-menus
