Unable to add pages on main navigation or delete pages.

I have been given an invitation by a client to edit his squarespace website. One of the instructions is to delete some of the pages under the main navigation and add new ones. I have watched plenty of videos where there is a + sign next to the main navigation where you can add pages. However, I do not have it one mine. Nor do I have the option to delete the pages. I am very confused. Is this because I do not have permission to certain features of SquareSpace not provided by the main host? I attached a loom video below for reference.

https://www.loom.com/share/e0cc3805da9f4998b3a7c2a8d5d3f488