To update the header navigation, please go to Appearances > Menus.
At the top left of the page, in the dropdown next to “Select a menu to edit:”, please make sure “Header Menu” is selected.
Under Menu Structure, you’ll see all the links in the header, with main menu links and dropdown menu links, arranged hierarchically. The dropdown links are placed below the main links and indented.
To edit any link, click the arrow on the right of it and update the text (Navigation Label) and/or link (URL), then click Save Menu to save changes.
To add a new link, click Custom Links, on the left hand side, then insert the URL and link text, then click Add To Menu. You can then drag the new link and drop it in the correct position within the hierarchy, then click Save Menu to save changes.