Dropdown links have to be placed in dropdown lists, however, it looks like you’ve cracked it already! You have a text link with a class of Nav Link in the top nav with ‘Text Link’ written. You can double click on the nav which opens up the dynamic element and then select the text. A menu option appears with on a cog to the right of the blue box. Click the cog which opens up link settings. Then click on the second icon along of a white page which lets you select a page of the site to link to from a dropdown list.
If you want to add another link you can drag a ‘Text Link’ into the nav. You’ll have to delete the existing Dropdown links I think.
Hope this helps, good luck.