I am not a developer but am trying to make changes to a WordPress site that was built by someone else. I have added a new page and want to add it to the navigation bar. However, when I go into appearances, menu there is no existing menu to edit. The pages column on the left-hand side appears and although I can tick pages, it is greyed out. I don't want to start a new menu as worry I will break someone that is currently there. Is there a way I can access the existing navigation bar to make changes? Thanks for your help
It's possible that the developer hard-coded the menu items in the theme. Check out the Appearance, Customize screen to see if there is a Menu choice in there somewhere.
It may also be that the active theme (assume it was by the developer) doesn't support Menus. That would be a warning sign to me that perhaps the theme is doing other non-standard theme stuff. You may need to find another theme, and use it. If you are not comfortable doing that yourself, you may need to find another (better) developer to help you out. But I'd check the new person's references first to make sure that they are doing things properly.